BUG: Fix a bug in plotting when using color array. #20726

doc/source/whatsnew/v0.23.0.txt

@@ -1159,6 +1159,7 @@ Plotting
 - Bug in formatting tick labels with ``datetime.time()`` and fractional seconds (:issue:`18478`).
 - :meth:`Series.plot.kde` has exposed the args ``ind`` and ``bw_method`` in the docstring (:issue:`18461`). The argument ``ind`` may now also be an integer (number of sample points).
 - :func:`DataFrame.plot` now supports multiple columns to the ``y`` argument (:issue:`19699`)
+- Bug in providing color array as color for a single plot (:issue:`20726`)
 
 
 Groupby/Resample/Rolling

pandas/plotting/_style.py

@@ -91,7 +91,7 @@ def _maybe_valid_colors(colors):
             # mpl will raise error any of them is invalid
             pass
 
-    if len(colors) != num_colors:
+    if len(colors) < num_colors:
         try:
             multiple = num_colors // len(colors) - 1
         except ZeroDivisionError:

pandas/tests/plotting/test_misc.py

@@ -313,3 +313,14 @@ def test_get_standard_colors_random_seed(self):
         color1 = _get_standard_colors(1, color_type='random')
         color2 = _get_standard_colors(1, color_type='random')
         assert color1 == color2
+
+    def test_get_standard_colors_no_appending(self):
+        # GH20726
+
+        # Make sure not to add more colors so that matplotlib can cycle
+        # correctly.
+        from pandas.plotting._style import _get_standard_colors
+        from matplotlib import cm
+        color_before = cm.gnuplot(range(5))
+        color_after = _get_standard_colors(1, color=color_before)
+        assert len(color_after) == len(color_before)