[ENH]: axes.labelcolor should use text.color by default

[anntzer]

Problem

rcParams["axes.titlecolor"] defaults to "auto", i.e. use text.color. On the other hand rcParams["axes.labelcolor"] (the color of the x/ylabels) defaults to "black", i.e. changing rcParams["text.color"] doesn't affect these labels).

Proposed solution

Add support for rcParams["axes.labelcolor"] = "auto", meaning to use the default text color, and make that the default rc value.

For bonus points: rcParams["x/ytick.labelcolor"] currently defaults to "inherit", which means to use the tick color. If we change here the spelling of "use the fallback" to "auto" (#28154), we could use that to also make "auto" mean "use rcParams["text.default"]" instead of rcParams["xtick.color"], which seems actually more consistent, especially if we also switch the rcParams["x/ytick.color"] to defaulting to the defaulf spines color (rcParams["axes.edgecolor"]) -- again, making the tick colors match the spine colors seems more important, to me, than making the tick colors and the ticklabel colors match by default, but ymmv.

[AnsonTran]

Hi @anntzer, would it make sense to provide support for "auto" in Text.set_color()? Something like this:

--- a/lib/matplotlib/text.py
+++ b/lib/matplotlib/text.py
@@ -987,11 +987,11 @@ class Text(Artist):
         ----------
         color : :mpltype:`color`
         """
-        # "auto" is only supported by axisartist, but we can just let it error
-        # out at draw time for simplicity.
-        if not cbook._str_equal(color, "auto"):
-            mpl.colors._check_color_like(color=color)
-        self._color = color
+        if color == None or cbook._str_lower_equal(color, "auto"):
+            self._color = mpl.rcParams["text.color"]
+        else:
+            self._color = color
+        mpl.colors._check_color_like(color=color)
         self.stale = True

[anntzer]

I think normal matplotlib semantics would be to just support None.

[AnsonTran]

I wanted to ask before I created a PR, since my current solution adds a bunch of checks in various parts of the code like this:

if not cbook._str_lower_equal(mpl.rcParams['axes.labelcolor'], 'auto'):
    self.label.set_color(mpl.rcParams['axes.labelcolor'])
else:
    self.label.set_color(mpl.rcParams['text.color'])

Whereas, supporting label.set_color("auto"), label.set_color(None), etc. could make it easier if we wanted to change the default in the future, and could simplify the code.

AnsonTran@e42586e