diff --git a/Lib/_colorize.py b/Lib/_colorize.py
index 9eb6f0933..d6673f669 100644
--- a/Lib/_colorize.py
+++ b/Lib/_colorize.py
@@ -1,13 +1,16 @@
-from __future__ import annotations
-import io
 import os
 import sys
 
+from collections.abc import Callable, Iterator, Mapping
+from dataclasses import dataclass, field, Field
+
 COLORIZE = True
 
+
 # types
 if False:
-    from typing import IO
+    from typing import IO, Self, ClassVar
+    _theme: Theme
 
 
 class ANSIColors:
@@ -17,11 +20,13 @@ class ANSIColors:
     BLUE = "\x1b[34m"
     CYAN = "\x1b[36m"
     GREEN = "\x1b[32m"
+    GREY = "\x1b[90m"
     MAGENTA = "\x1b[35m"
     RED = "\x1b[31m"
     WHITE = "\x1b[37m"  # more like LIGHT GRAY
     YELLOW = "\x1b[33m"
 
+    BOLD = "\x1b[1m"
     BOLD_BLACK = "\x1b[1;30m"  # DARK GRAY
     BOLD_BLUE = "\x1b[1;34m"
     BOLD_CYAN = "\x1b[1;36m"
@@ -60,13 +65,196 @@ class ANSIColors:
     INTENSE_BACKGROUND_YELLOW = "\x1b[103m"
 
 
+ColorCodes = set()
 NoColors = ANSIColors()
 
-for attr in dir(NoColors):
+for attr, code in ANSIColors.__dict__.items():
     if not attr.startswith("__"):
+        ColorCodes.add(code)
         setattr(NoColors, attr, "")
 
 
+#
+# Experimental theming support (see gh-133346)
+#
+
+# - Create a theme by copying an existing `Theme` with one or more sections
+#   replaced, using `default_theme.copy_with()`;
+# - create a theme section by copying an existing `ThemeSection` with one or
+#   more colors replaced, using for example `default_theme.syntax.copy_with()`;
+# - create a theme from scratch by instantiating a `Theme` data class with
+#   the required sections (which are also dataclass instances).
+#
+# Then call `_colorize.set_theme(your_theme)` to set it.
+#
+# Put your theme configuration in $PYTHONSTARTUP for the interactive shell,
+# or sitecustomize.py in your virtual environment or Python installation for
+# other uses.  Your applications can call `_colorize.set_theme()` too.
+#
+# Note that thanks to the dataclasses providing default values for all fields,
+# creating a new theme or theme section from scratch is possible without
+# specifying all keys.
+#
+# For example, here's a theme that makes punctuation and operators less prominent:
+#
+#   try:
+#       from _colorize import set_theme, default_theme, Syntax, ANSIColors
+#   except ImportError:
+#       pass
+#   else:
+#       theme_with_dim_operators = default_theme.copy_with(
+#           syntax=Syntax(op=ANSIColors.INTENSE_BLACK),
+#       )
+#       set_theme(theme_with_dim_operators)
+#       del set_theme, default_theme, Syntax, ANSIColors, theme_with_dim_operators
+#
+# Guarding the import ensures that your .pythonstartup file will still work in
+# Python 3.13 and older. Deleting the variables ensures they don't remain in your
+# interactive shell's global scope.
+
+class ThemeSection(Mapping[str, str]):
+    """A mixin/base class for theme sections.
+
+    It enables dictionary access to a section, as well as implements convenience
+    methods.
+    """
+
+    # The two types below are just that: types to inform the type checker that the
+    # mixin will work in context of those fields existing
+    __dataclass_fields__: ClassVar[dict[str, Field[str]]]
+    _name_to_value: Callable[[str], str]
+
+    def __post_init__(self) -> None:
+        name_to_value = {}
+        for color_name in self.__dataclass_fields__:
+            name_to_value[color_name] = getattr(self, color_name)
+        super().__setattr__('_name_to_value', name_to_value.__getitem__)
+
+    def copy_with(self, **kwargs: str) -> Self:
+        color_state: dict[str, str] = {}
+        for color_name in self.__dataclass_fields__:
+            color_state[color_name] = getattr(self, color_name)
+        color_state.update(kwargs)
+        return type(self)(**color_state)
+
+    @classmethod
+    def no_colors(cls) -> Self:
+        color_state: dict[str, str] = {}
+        for color_name in cls.__dataclass_fields__:
+            color_state[color_name] = ""
+        return cls(**color_state)
+
+    def __getitem__(self, key: str) -> str:
+        return self._name_to_value(key)
+
+    def __len__(self) -> int:
+        return len(self.__dataclass_fields__)
+
+    def __iter__(self) -> Iterator[str]:
+        return iter(self.__dataclass_fields__)
+
+
+@dataclass(frozen=True, kw_only=True)
+class Argparse(ThemeSection):
+    usage: str = ANSIColors.BOLD_BLUE
+    prog: str = ANSIColors.BOLD_MAGENTA
+    prog_extra: str = ANSIColors.MAGENTA
+    heading: str = ANSIColors.BOLD_BLUE
+    summary_long_option: str = ANSIColors.CYAN
+    summary_short_option: str = ANSIColors.GREEN
+    summary_label: str = ANSIColors.YELLOW
+    summary_action: str = ANSIColors.GREEN
+    long_option: str = ANSIColors.BOLD_CYAN
+    short_option: str = ANSIColors.BOLD_GREEN
+    label: str = ANSIColors.BOLD_YELLOW
+    action: str = ANSIColors.BOLD_GREEN
+    reset: str = ANSIColors.RESET
+
+
+@dataclass(frozen=True)
+class Syntax(ThemeSection):
+    prompt: str = ANSIColors.BOLD_MAGENTA
+    keyword: str = ANSIColors.BOLD_BLUE
+    keyword_constant: str = ANSIColors.BOLD_BLUE
+    builtin: str = ANSIColors.CYAN
+    comment: str = ANSIColors.RED
+    string: str = ANSIColors.GREEN
+    number: str = ANSIColors.YELLOW
+    op: str = ANSIColors.RESET
+    definition: str = ANSIColors.BOLD
+    soft_keyword: str = ANSIColors.BOLD_BLUE
+    reset: str = ANSIColors.RESET
+
+
+@dataclass(frozen=True)
+class Traceback(ThemeSection):
+    type: str = ANSIColors.BOLD_MAGENTA
+    message: str = ANSIColors.MAGENTA
+    filename: str = ANSIColors.MAGENTA
+    line_no: str = ANSIColors.MAGENTA
+    frame: str = ANSIColors.MAGENTA
+    error_highlight: str = ANSIColors.BOLD_RED
+    error_range: str = ANSIColors.RED
+    reset: str = ANSIColors.RESET
+
+
+@dataclass(frozen=True)
+class Unittest(ThemeSection):
+    passed: str = ANSIColors.GREEN
+    warn: str = ANSIColors.YELLOW
+    fail: str = ANSIColors.RED
+    fail_info: str = ANSIColors.BOLD_RED
+    reset: str = ANSIColors.RESET
+
+
+@dataclass(frozen=True)
+class Theme:
+    """A suite of themes for all sections of Python.
+
+    When adding a new one, remember to also modify `copy_with` and `no_colors`
+    below.
+    """
+    argparse: Argparse = field(default_factory=Argparse)
+    syntax: Syntax = field(default_factory=Syntax)
+    traceback: Traceback = field(default_factory=Traceback)
+    unittest: Unittest = field(default_factory=Unittest)
+
+    def copy_with(
+        self,
+        *,
+        argparse: Argparse | None = None,
+        syntax: Syntax | None = None,
+        traceback: Traceback | None = None,
+        unittest: Unittest | None = None,
+    ) -> Self:
+        """Return a new Theme based on this instance with some sections replaced.
+
+        Themes are immutable to protect against accidental modifications that
+        could lead to invalid terminal states.
+        """
+        return type(self)(
+            argparse=argparse or self.argparse,
+            syntax=syntax or self.syntax,
+            traceback=traceback or self.traceback,
+            unittest=unittest or self.unittest,
+        )
+
+    @classmethod
+    def no_colors(cls) -> Self:
+        """Return a new Theme where colors in all sections are empty strings.
+
+        This allows writing user code as if colors are always used. The color
+        fields will be ANSI color code strings when colorization is desired
+        and possible, and empty strings otherwise.
+        """
+        return cls(
+            argparse=Argparse.no_colors(),
+            syntax=Syntax.no_colors(),
+            traceback=Traceback.no_colors(),
+            unittest=Unittest.no_colors(),
+        )
+
+
 def get_colors(
     colorize: bool = False, *, file: IO[str] | IO[bytes] | None = None
 ) -> ANSIColors:
@@ -76,22 +264,37 @@ def get_colors(
         return NoColors
 
 
+def decolor(text: str) -> str:
+    """Remove ANSI color codes from a string."""
+    for code in ColorCodes:
+        text = text.replace(code, "")
+    return text
+
+
 def can_colorize(*, file: IO[str] | IO[bytes] | None = None) -> bool:
+
+    def _safe_getenv(k: str, fallback: str | None = None) -> str | None:
+        """Exception-safe environment retrieval. See gh-128636."""
+        try:
+            return os.environ.get(k, fallback)
+        except Exception:
+            return fallback
+
     if file is None:
         file = sys.stdout
 
     if not sys.flags.ignore_environment:
-        if os.environ.get("PYTHON_COLORS") == "0":
+        if _safe_getenv("PYTHON_COLORS") == "0":
             return False
-        if os.environ.get("PYTHON_COLORS") == "1":
+        if _safe_getenv("PYTHON_COLORS") == "1":
             return True
-    if os.environ.get("NO_COLOR"):
+    if _safe_getenv("NO_COLOR"):
         return False
     if not COLORIZE:
         return False
-    if os.environ.get("FORCE_COLOR"):
+    if _safe_getenv("FORCE_COLOR"):
         return True
-    if os.environ.get("TERM") == "dumb":
+    if _safe_getenv("TERM") == "dumb":
         return False
 
     if not hasattr(file, "fileno"):
@@ -108,5 +311,45 @@ def can_colorize(*, file: IO[str] | IO[bytes] | None = None) -> bool:
 
     try:
         return os.isatty(file.fileno())
-    except io.UnsupportedOperation:
+    except OSError:
         return hasattr(file, "isatty") and file.isatty()
+
+
+default_theme = Theme()
+theme_no_color = default_theme.no_colors()
+
+
+def get_theme(
+    *,
+    tty_file: IO[str] | IO[bytes] | None = None,
+    force_color: bool = False,
+    force_no_color: bool = False,
+) -> Theme:
+    """Returns the currently set theme, potentially in a zero-color variant.
+
+    In cases where colorizing is not possible (see `can_colorize`), the returned
+    theme contains all empty strings in all color definitions.
+    See `Theme.no_colors()` for more information.
+
+    It is recommended not to cache the result of this function for extended
+    periods of time because the user might influence theme selection by
+    the interactive shell, a debugger, or application-specific code. The
+    environment (including environment variable state and console configuration
+    on Windows) can also change in the course of the application life cycle.
+    """
+    if force_color or (not force_no_color and
+                       can_colorize(file=tty_file)):
+        return _theme
+    return theme_no_color
+
+
+def set_theme(t: Theme) -> None:
+    global _theme
+
+    if not isinstance(t, Theme):
+        raise ValueError(f"Expected Theme object, found {t}")
+
+    _theme = t
+
+
+set_theme(default_theme)
diff --git a/Lib/test/test__colorize.py b/Lib/test/test__colorize.py
index b2f0bb138..31dc60fec 100644
--- a/Lib/test/test__colorize.py
+++ b/Lib/test/test__colorize.py
@@ -1,4 +1,5 @@
 import contextlib
+import dataclasses
 import io
 import sys
 import unittest
@@ -21,6 +22,42 @@ def supports_virtual_terminal():
         return contextlib.nullcontext()
 
 
+class TestTheme(unittest.TestCase):
+
+    @unittest.expectedFailure # TODO: RUSTPYTHON
+    def test_attributes(self):
+        # only theme configurations attributes by default
+        for field in dataclasses.fields(_colorize.Theme):
+            with self.subTest(field.name):
+                self.assertIsSubclass(field.type, _colorize.ThemeSection)
+                self.assertIsNotNone(field.default_factory)
+
+    def test_copy_with(self):
+        theme = _colorize.Theme()
+
+        copy = theme.copy_with()
+        self.assertEqual(theme, copy)
+
+        unittest_no_colors = _colorize.Unittest.no_colors()
+        copy = theme.copy_with(unittest=unittest_no_colors)
+        self.assertEqual(copy.argparse, theme.argparse)
+        self.assertEqual(copy.syntax, theme.syntax)
+        self.assertEqual(copy.traceback, theme.traceback)
+        self.assertEqual(copy.unittest, unittest_no_colors)
+
+    def test_no_colors(self):
+        # idempotence test
+        theme_no_colors = _colorize.Theme().no_colors()
+        theme_no_colors_no_colors = theme_no_colors.no_colors()
+        self.assertEqual(theme_no_colors, theme_no_colors_no_colors)
+
+        # attributes check
+        for section in dataclasses.fields(_colorize.Theme):
+            with self.subTest(section.name):
+                section_theme = getattr(theme_no_colors, section.name)
+                self.assertEqual(section_theme, section.type.no_colors())
+
+
 class TestColorizeFunction(unittest.TestCase):
     def test_colorized_detection_checks_for_environment_variables(self):
         def check(env, fallback, expected):
@@ -129,6 +166,17 @@ class TestColorizeFunction(unittest.TestCase):
                 file.isatty.return_value = False
                 self.assertEqual(_colorize.can_colorize(file=file), False)
 
+            # The documentation for file.fileno says:
+            # > An OSError is raised if the IO object does not use a file descriptor.
+            # gh-141570: Check OSError is caught and handled
+            with unittest.mock.patch("os.isatty", side_effect=ZeroDivisionError):
+                file = unittest.mock.MagicMock()
+                file.fileno.side_effect = OSError
+                file.isatty.return_value = True
+                self.assertEqual(_colorize.can_colorize(file=file), True)
+                file.isatty.return_value = False
+                self.assertEqual(_colorize.can_colorize(file=file), False)
+
 
 if __name__ == "__main__":
     unittest.main()