Series.plot doesn't allow color=None (pandas-dev#51967)

Author: dannyi96

doc/source/whatsnew/v2.1.0.rst

@@ -198,7 +198,7 @@ Period
 
 Plotting
 ^^^^^^^^
--
+- Bug in :meth:`Series.plot` when invoked with ``color=None`` (:issue:`51953`)
 -
 
 Groupby/resample/rolling

pandas/plotting/_matplotlib/core.py

@@ -377,6 +377,7 @@ def _validate_color_args(self):
         if (
             "color" in self.kwds
             and self.nseries == 1
+            and self.kwds["color"] is not None
             and not is_list_like(self.kwds["color"])
         ):
             # support series.plot(color='green')

pandas/tests/plotting/frame/test_frame_color.py

@@ -659,3 +659,10 @@ def test_invalid_colormap(self):
         msg = "(is not a valid value)|(is not a known colormap)"
         with pytest.raises((ValueError, KeyError), match=msg):
             df.plot(colormap="invalid_colormap")
+
+    def test_dataframe_none_color(self):
+        # GH51953
+        df = DataFrame([[1, 2, 3]])
+        ax = df.plot(color=None)
+        expected = self._unpack_cycler(self.plt.rcParams)[:3]
+        self._check_colors(ax.get_lines(), linecolors=expected)

pandas/tests/plotting/test_series.py

@@ -848,3 +848,10 @@ def test_timedelta_index(self, index):
         xlims = (3, 1)
         ax = Series([1, 2], index=index).plot(xlim=(xlims))
         assert ax.get_xlim() == (3, 1)
+
+    def test_series_none_color(self):
+        # GH51953
+        series = Series([1, 2, 3])
+        ax = series.plot(color=None)
+        expected = self._unpack_cycler(self.plt.rcParams)[:1]
+        self._check_colors(ax.get_lines(), linecolors=expected)