Backport PR matplotlib#28993: FIX: contourf hatches use multiple edgecolors

Author: rcomer

lib/matplotlib/contour.py

@@ -1415,12 +1415,16 @@ def draw(self, renderer):
             super().draw(renderer)
             return
         # In presence of hatching, draw contours one at a time.
+        edgecolors = self.get_edgecolors()
+        if edgecolors.size == 0:
+            edgecolors = ("none",)
         for idx in range(n_paths):
             with cbook._setattr_cm(self, _paths=[paths[idx]]), self._cm_set(
                 hatch=self.hatches[idx % len(self.hatches)],
                 array=[self.get_array()[idx]],
                 linewidths=[self.get_linewidths()[idx % len(self.get_linewidths())]],
                 linestyles=[self.get_linestyles()[idx % len(self.get_linestyles())]],
+                edgecolors=edgecolors[idx % len(edgecolors)],
             ):
                 super().draw(renderer)
 

lib/matplotlib/tests/baseline_images/test_contour/contourf_hatch_colors.png

@@ -198,6 +198,14 @@ def test_given_colors_levels_and_extends(split_collections):
     _maybe_split_collections(split_collections)
 
 
+@image_comparison(['contourf_hatch_colors'],
+                  remove_text=True, style='mpl20', extensions=['png'])
+def test_hatch_colors():
+    fig, ax = plt.subplots()
+    cf = ax.contourf([[0, 1], [1, 2]], hatches=['-', '/', '\\', '//'], cmap='gray')
+    cf.set_edgecolors(["blue", "grey", "yellow", "red"])
+
+
 @pytest.mark.parametrize("split_collections", [False, True])
 @image_comparison(['contour_log_locator.svg'], style='mpl20', remove_text=False)
 def test_log_locator_levels(split_collections):