matplotlib · Tranquilled · Oct 5, 2020 · Oct 6, 2020 · Oct 6, 2020 · Oct 6, 2020
diff --git a/doc/api/next_api_changes/behavior/18668-LL.rst b/doc/api/next_api_changes/behavior/18668-LL.rst
@@ -0,0 +1,8 @@
+Shadow parameter for Legend can be colorlike or bool
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The *shadow* parameter can now be any colorlike in addition to
+a bool. If it is neither, a ValueError is thrown.
+
+An accessory validation function `~.rcsetup.validate_color_or_bool`
+has also been added, which preferentially returns a color.
diff --git a/doc/users/next_whats_new/explicit_shadow_color.rst b/doc/users/next_whats_new/explicit_shadow_color.rst
@@ -0,0 +1,12 @@
+Legend shadow colors can be explicitly defined
+----------------------------------------------
+
+The *shadow* parameter for the Legend constructor now
+accepts both color and bool. If it is a bool, the
+behavior is exactly the same as before.
+Any colorlike value sets the shadow to that color,
+subject to the same transparency effect that the default
+facecolor undergoes.
+
+An accessory validation function `~.rcsetup.validate_color_or_bool`
+has also been added, which preferentially returns a color.
diff --git a/lib/matplotlib/legend.py b/lib/matplotlib/legend.py
@@ -31,6 +31,7 @@
 from matplotlib import _api, docstring, colors
 from matplotlib.artist import Artist, allow_rasterization
 from matplotlib.cbook import silent_list
+from matplotlib.colors import is_color_like
 from matplotlib.font_manager import FontProperties
 from matplotlib.lines import Line2D
 from matplotlib.patches import (Patch, Rectangle, Shadow, FancyBboxPatch,
@@ -208,8 +209,9 @@ def _update_bbox_to_anchor(self, loc_in_canvas):
     Whether round edges should be enabled around the `~.FancyBboxPatch` which
     makes up the legend's background.
 
-shadow : bool, default: :rc:`legend.shadow`
+shadow : bool or color, default: :rc:`legend.shadow`
     Whether to draw a shadow behind the legend.
+    If value is a color, a shadow of that color will be applied.
 
 framealpha : float, default: :rc:`legend.framealpha`
     The alpha transparency of the legend's background.
@@ -514,7 +516,6 @@ def __init__(self, parent, handles, labels,
         self._draggable = None
 
         # set the text color
-
         color_getters = {  # getter function depends on line or patch
             'linecolor':       ['get_color',           'get_facecolor'],
             'markerfacecolor': ['get_markerfacecolor', 'get_facecolor'],
@@ -607,8 +608,14 @@ def draw(self, renderer):
         self.legendPatch.set_bounds(bbox.x0, bbox.y0, bbox.width, bbox.height)
         self.legendPatch.set_mutation_scale(fontsize)
 
-        if self.shadow:
+        if is_color_like(self.shadow):
+            Shadow(self.legendPatch, 2, -2, color=self.shadow).draw(renderer)
+        elif self.shadow is True:
             Shadow(self.legendPatch, 2, -2).draw(renderer)
+        elif self.shadow is False:
+            pass
+        else:
+            raise ValueError('Shadow must be a valid color or bool.')
 
         self.legendPatch.draw(renderer)
         self._legend_box.draw(renderer)

diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
@@ -146,6 +146,18 @@ def validate_bool(b):
         raise ValueError('Could not convert "%s" to bool' % b)
 
 
+def validate_color_or_bool(c):
+    """Convert c to color (preferentially) or bool"""
+    try:
+        return validate_color(c)
+    except ValueError:
+        pass
+    try:
+        return validate_bool(c)
+    except ValueError:
+        raise ValueError(f'Could not convert {c} to color or bool.')
+
+
 @_api.deprecated("3.3")
 def validate_bool_maybe_none(b):
     """Convert b to ``bool`` or raise, passing through *None*."""
@@ -1229,7 +1241,7 @@ def _convert_validator_spec(key, conv):
     "legend.title_fontsize": validate_fontsize_None,
      # the relative size of legend markers vs. original
     "legend.markerscale":    validate_float,
-    "legend.shadow":         validate_bool,
+    "legend.shadow":         validate_color_or_bool,
      # whether or not to draw a frame around legend
     "legend.frameon":        validate_bool,
      # alpha value of the legend frame