BUG: Respect color argument in bar plot (#17360)

This affect Series-like barplots with user-defined colors. We were always
treating them as dataframe-like, with one color per column.

Author: TomAugspurger

doc/source/whatsnew/v0.21.0.txt

@@ -524,6 +524,8 @@ Plotting
 ^^^^^^^^
 - Bug in plotting methods using ``secondary_y`` and ``fontsize`` not setting secondary axis font size (:issue:`12565`)
 - Bug when plotting ``timedelta`` and ``datetime`` dtypes on y-axis (:issue:`16953`)
+- Bug in ``Series.plot.bar`` or ``DataFramee.plot.bar`` with ``y`` not respecting user-passed ``color`` (:issue:`16822`)
+
 
 Groupby/Resample/Rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^

pandas/plotting/_core.py

@@ -1150,6 +1150,9 @@ class BarPlot(MPLPlot):
     orientation = 'vertical'
 
     def __init__(self, data, **kwargs):
+        # we have to treat a series differently than a
+        # 1-column DataFrame w.r.t. color handling
+        self._is_series = isinstance(data, ABCSeries)
         self.bar_width = kwargs.pop('width', 0.5)
         pos = kwargs.pop('position', 0.5)
         kwargs.setdefault('align', 'center')
@@ -1204,7 +1207,10 @@ def _make_plot(self):
         for i, (label, y) in enumerate(self._iter_data(fillna=0)):
             ax = self._get_ax(i)
             kwds = self.kwds.copy()
-            kwds['color'] = colors[i % ncolors]
+            if self._is_series:
+                kwds['color'] = colors
+            else:
+                kwds['color'] = colors[i % ncolors]
 
             errors = self._get_errorbars(label=label, index=i)
             kwds = dict(kwds, **errors)

pandas/tests/plotting/test_frame.py

@@ -807,6 +807,20 @@ def test_bar_colors(self):
         self._check_colors(ax.patches[::5], facecolors=['green'] * 5)
         tm.close()
 
+    def test_bar_user_colors(self):
+        df = pd.DataFrame({"A": range(4),
+                           "B": range(1, 5),
+                           "color": ['red', 'blue', 'blue', 'red']})
+        # This should *only* work when `y` is specified, else
+        # we use one color per column
+        ax = df.plot.bar(y='A', color=df['color'])
+        result = [p.get_facecolor() for p in ax.patches]
+        expected = [(1., 0., 0., 1.),
+                    (0., 0., 1., 1.),
+                    (0., 0., 1., 1.),
+                    (1., 0., 0., 1.)]
+        assert result == expected
+
     @pytest.mark.slow
     def test_bar_linewidth(self):
         df = DataFrame(randn(5, 5))

pandas/tests/plotting/test_series.py

@@ -258,6 +258,16 @@ def test_bar_ignore_index(self):
         ax = df.plot.bar(use_index=False, ax=ax)
         self._check_text_labels(ax.get_xticklabels(), ['0', '1', '2', '3'])
 
+    def test_bar_user_colors(self):
+        s = Series([1, 2, 3, 4])
+        ax = s.plot.bar(color=['red', 'blue', 'blue', 'red'])
+        result = [p.get_facecolor() for p in ax.patches]
+        expected = [(1., 0., 0., 1.),
+                    (0., 0., 1., 1.),
+                    (0., 0., 1., 1.),
+                    (1., 0., 0., 1.)]
+        assert result == expected
+
     def test_rotation(self):
         df = DataFrame(randn(5, 5))
         # Default rot 0