Fix validation of Line2D color.

anntzer · anntzer · commit 2cdcc03f32d6 · 2021-05-10T19:34:10.000+02:00
We don't actually support color="auto" (we only support mfc="auto" and
mec="auto", which mean "use the main color") -- with the sole exception
of axisartist Ticks, which is a subclass that has special handling for
"auto".

This can easily be tested using `plt.plot([1, 2], c="auto")` which
crashes.
diff --git a/lib/matplotlib/lines.py b/lib/matplotlib/lines.py
@@ -1027,8 +1027,7 @@ def set_color(self, color):
         ----------
         color : color
         """
-        if not cbook._str_equal(color, 'auto'):
-            mcolors._check_color_like(color=color)
+        mcolors._check_color_like(color=color)
         self._color = color
         self.stale = True
 
diff --git a/lib/mpl_toolkits/axisartist/axis_artist.py b/lib/mpl_toolkits/axisartist/axis_artist.py
@@ -75,10 +75,10 @@
 
 import numpy as np
 
-from matplotlib import _api, rcParams
+from matplotlib import _api, cbook, rcParams
 import matplotlib.artist as martist
+import matplotlib.colors as mcolors
 import matplotlib.text as mtext
-
 from matplotlib.collections import LineCollection
 from matplotlib.lines import Line2D
 from matplotlib.patches import PathPatch
@@ -134,6 +134,14 @@ def get_ref_artist(self):
         # docstring inherited
         return self._axis.majorTicks[0].tick1line
 
+    def set_color(self, color):
+        # docstring inherited
+        # Unlike the base Line2D.set_color, this also supports "auto".
+        if not cbook._str_equal(color, "auto"):
+            mcolors._check_color_like(color=color)
+        self._color = color
+        self.stale = True
+
     def get_color(self):
         return self.get_attribute_from_ref_artist("color")
 
