PLT: Color attributes of medianprops etc are lost in df.boxplot and df.plot.boxplot

doc/source/whatsnew/v1.1.0.rst

@@ -192,6 +192,8 @@ Plotting
 
 - :func:`.plot` for line/bar now accepts color by dictonary (:issue:`8193`).
 -
+- Bug in :meth:`DataFrame.boxplot` and :meth:`DataFrame.plot.boxplot` lost color attributes of ``medianprops``, ``whiskerprops``, ``capprops`` and ``medianprops`` (:issue:`30346`)
+
 
 Groupby/resample/rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^

pandas/plotting/_matplotlib/boxplot.py

@@ -107,10 +107,16 @@ def maybe_color_bp(self, bp):
             medians = self.color or self._medians_c
             caps = self.color or self._caps_c
 
-        setp(bp["boxes"], color=boxes, alpha=1)
-        setp(bp["whiskers"], color=whiskers, alpha=1)
-        setp(bp["medians"], color=medians, alpha=1)
-        setp(bp["caps"], color=caps, alpha=1)
+        # GH 30346, when users specifying those arguments explicitly, our defaults
+        # for these four kwargs should be overridden; if not, use Pandas settings
+        if not self.kwds.get("boxprops"):
+            setp(bp["boxes"], color=boxes, alpha=1)
+        if not self.kwds.get("whiskerprops"):
+            setp(bp["whiskers"], color=whiskers, alpha=1)
+        if not self.kwds.get("medianprops"):
+            setp(bp["medians"], color=medians, alpha=1)
+        if not self.kwds.get("capprops"):
+            setp(bp["caps"], color=caps, alpha=1)
 
     def _make_plot(self):
         if self.subplots:
@@ -275,11 +281,17 @@ def _get_colors():
 
         return result
 
-    def maybe_color_bp(bp):
-        setp(bp["boxes"], color=colors[0], alpha=1)
-        setp(bp["whiskers"], color=colors[1], alpha=1)
-        setp(bp["medians"], color=colors[2], alpha=1)
-        setp(bp["caps"], color=colors[3], alpha=1)
+    def maybe_color_bp(bp, **kwds):
+        # GH 30346, when users specifying those arguments explicitly, our defaults
+        # for these four kwargs should be overridden; if not, use Pandas settings
+        if not kwds.get("boxprops"):
+            setp(bp["boxes"], color=colors[0], alpha=1)
+        if not kwds.get("whiskerprops"):
+            setp(bp["whiskers"], color=colors[1], alpha=1)
+        if not kwds.get("medianprops"):
+            setp(bp["medians"], color=colors[2], alpha=1)
+        if not kwds.get("capprops"):
+            setp(bp["caps"], color=colors[3], alpha=1)
 
     def plot_group(keys, values, ax):
         keys = [pprint_thing(x) for x in keys]
@@ -291,7 +303,7 @@ def plot_group(keys, values, ax):
             ax.set_xticklabels(keys, rotation=rot)
         else:
             ax.set_yticklabels(keys, rotation=rot)
-        maybe_color_bp(bp)
+        maybe_color_bp(bp, **kwds)
 
         # Return axes in multiplot case, maybe revisit later # 985
         if return_type == "dict":

pandas/tests/plotting/test_boxplot_method.py

@@ -203,6 +203,23 @@ def test_color_kwd_errors(self, dict_colors, msg):
         with pytest.raises(ValueError, match=msg):
             df.boxplot(color=dict_colors, return_type="dict")
 
+    @pytest.mark.parametrize(
+        "props, expected",
+        [
+            ("boxprops", "boxes"),
+            ("whiskerprops", "whiskers"),
+            ("capprops", "caps"),
+            ("medianprops", "medians"),
+        ],
+    )
+    def test_specified_props_kwd(self, props, expected):
+        # GH 30346
+        df = DataFrame({k: np.random.random(100) for k in "ABC"})
+        kwd = {props: dict(color="C1")}
+        result = df.boxplot(return_type="dict", **kwd)
+
+        assert result[expected][0].get_color() == "C1"
+
 
 @td.skip_if_no_mpl
 class TestDataFrameGroupByPlots(TestPlotBase):

pandas/tests/plotting/test_frame.py

@@ -2352,6 +2352,23 @@ def _check_colors(bp, box_c, whiskers_c, medians_c, caps_c="k", fliers_c=None):
             # Color contains invalid key results in ValueError
             df.plot.box(color=dict(boxes="red", xxxx="blue"))
 
+    @pytest.mark.parametrize(
+        "props, expected",
+        [
+            ("boxprops", "boxes"),
+            ("whiskerprops", "whiskers"),
+            ("capprops", "caps"),
+            ("medianprops", "medians"),
+        ],
+    )
+    def test_specified_props_kwd_plot_box(self, props, expected):
+        # GH 30346
+        df = DataFrame({k: np.random.random(100) for k in "ABC"})
+        kwd = {props: dict(color="C1")}
+        result = df.plot.box(return_type="dict", **kwd)
+
+        assert result[expected][0].get_color() == "C1"
+
     def test_default_color_cycle(self):
         import matplotlib.pyplot as plt
         import cycler