Move whatsnew and add more test

doc/source/whatsnew/v0.23.0.txt

@@ -1342,7 +1342,6 @@ 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

doc/source/whatsnew/v0.24.0.txt

@@ -680,6 +680,8 @@ Plotting
 
 - Bug in :func:`DataFrame.plot.scatter` and :func:`DataFrame.plot.hexbin` caused x-axis label and ticklabels to disappear when colorbar was on in IPython inline backend (:issue:`10611`, :issue:`10678`, and :issue:`20455`)
 - Bug in plotting a Series with datetimes using :func:`matplotlib.axes.Axes.scatter` (:issue:`22039`)
+- Bug in validating color parameter caused extra color to be appended to the given color array. This happened to multiple plotting functions that plotting with matplotlib. (:issue:`20726`)
+
 
 Groupby/Resample/Rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^

pandas/tests/plotting/test_misc.py

@@ -323,3 +323,15 @@ def test_get_standard_colors_no_appending(self):
  color_before = cm.gnuplot(range(5))
  color_after = _get_standard_colors(1, color=color_before)
  assert len(color_after) == len(color_before)
+
+ # Original bug report example.
+ import numpy as np
+ import pandas as pd
+
+ df = pd.DataFrame(np.abs(np.random.randn(48, 4)),
+ columns=list("ABCD"))
+
+ color_list = cm.gnuplot(np.linspace(0, 1, 16))
+ p = df.A.plot.bar(figsize=(16, 7), color=color_list)
+ assert (p.patches[1].get_facecolor()
+ == p.patches[17].get_facecolor())