Allow disabling color inheritance for TeX mobjects

docs/source/guides/using_text.rst

@@ -384,6 +384,52 @@ we have to add it manually.
             )
             self.add(tex)
 
+You can use the ``xcolor`` package to apply colors within TeX, but to do this
+you have to explicitly state that you want to preserve these colors (as the
+default is to override them with whatever the default :class:`~.VMobject`
+color is):
+
+.. manim:: XColor
+    :save_last_frame:
+
+    class XColor(Scene):
+        def construct(self):
+            myTemplate = TexTemplate()
+            myTemplate.add_to_preamble(r"\usepackage{xcolor}")
+            tex = Tex(
+                r"\textcolor{white}{Hello} \textcolor{yellow}{\LaTeX}",
+                tex_template=myTemplate,
+                font_size=144,
+                preserve_colors=True,
+            )
+            self.add(tex)
+
+You can use :func:`manim.mobject.mobject.Mobject.set_default` to make this the
+default:
+
+.. manim:: DefaultTexTemplate
+    :save_last_frame:
+
+    class DefaultTexTemplate(Scene):
+        def construct(self):
+            myTemplate = TexTemplate()
+            myTemplate.add_to_preamble(r"\usepackage{xcolor}")
+            myTemplate.add_to_document(r"\color{white}")
+
+            Tex.set_default(
+                tex_template=myTemplate,
+                preserve_colors=True
+            )
+
+            tex = Tex(
+                r"Hello \textcolor{yellow}{\LaTeX}",
+                font_size=144,
+            )
+            self.add(tex)
+
+            # Restore original defaults, to avoid breaking documentation
+            Tex.set_default()
+
 Substrings and parts
 ====================
 

manim/mobject/text/tex_mobject.py

@@ -44,6 +44,36 @@
 class SingleStringMathTex(SVGMobject):
     """Elementary building block for rendering text with LaTeX.
 
+    Parameters
+    ----------
+    tex_string
+        The TeX source string to render.
+    stroke_width
+        The stroke width of the mobject. If ``None`` (the default),
+        the stroke width values set in the generated SVG file are used.
+    should_center
+        Whether or not the mobject should be centered after
+        being imported.
+    height
+    organize_left_to_right
+    tex_environment
+        The TeX environment to wrap the string in.
+    tex_template
+        The TeX template to use when rendering the string.
+    font_size
+    preserve_colors
+        If ``False`` (the default), the mobject is recolored based on
+        the default :class:`~.VMobject` color.
+        If ``True``, the colors in the TeX document are used.
+
+        .. warning::
+            By default, TeX strings are coloured black, meaning they
+            will be invisible against a black background.
+            If you want to use this option, it is recommended to set
+            a default color in TeX.
+    kwargs
+        Further arguments passed to the parent class.
+
     Tests
     -----
     Check that creating a :class:`~.SingleStringMathTex` object works::
@@ -62,9 +92,10 @@ def __init__(
         tex_environment: str = "align*",
         tex_template: TexTemplate | None = None,
         font_size: float = DEFAULT_FONT_SIZE,
+        preserve_colors: bool = False,
         **kwargs,
     ):
-        if kwargs.get("color") is None:
+        if kwargs.get("color") is None and not preserve_colors:
             # makes it so that color isn't explicitly passed for these mobs,
             # and can instead inherit from the parent
             kwargs["color"] = VMobject().color

tests/test_graphical_units/test_tex_mobject.py

@@ -9,12 +9,23 @@
 @frames_comparison
 def test_color_inheritance(scene):
     """Test that Text and MarkupText correctly inherit colour from
-    their parent class."""
+    their parent class when the preserve_colors argument is unset."""
 
     VMobject.set_default(color=RED)
-    tex = Tex("test color inheritance")
-    mathtex = MathTex("test color inheritance")
-    vgr = VGroup(tex, mathtex).arrange()
+
+    template = config.tex_template.copy()
+    template.add_to_preamble(r"\usepackage{xcolor}")
+
+    text = r"test color \textcolor{green}{inheritance}"
+
+    tex_inherit = Tex(text, tex_template=template)
+    mathtex_inherit = MathTex(text, tex_template=template)
+    tex_preserve = Tex(text, tex_template=template, preserve_colors=True)
+    mathtex_preserve = MathTex(text, tex_template=template, preserve_colors=True)
+
+    vgr = VGroup(tex_inherit, mathtex_inherit, tex_preserve, mathtex_preserve).arrange(
+        DOWN
+    )
     VMobject.set_default()
 
     scene.add(vgr)