diff --git a/lib/mpl_toolkits/mplot3d/art3d.py b/lib/mpl_toolkits/mplot3d/art3d.py
index 0888853df37e..cf825dfa053a 100644
--- a/lib/mpl_toolkits/mplot3d/art3d.py
+++ b/lib/mpl_toolkits/mplot3d/art3d.py
@@ -800,7 +800,17 @@ def _maybe_depth_shade_and_sort_colors(self, color_array):
         )
         if len(color_array) > 1:
             color_array = color_array[self._z_markers_idx]
-        return mcolors.to_rgba_array(color_array, self._alpha)
+
+        if color_array.shape[1] == 3: # color_array is RGB instead of RGBA
+            return mcolors.to_rgba_array(color_array, self._alpha)
+        
+        converted_alphas = (
+            color_array[:, 3] * self._alpha
+            if self._alpha is not None
+            else color_array[:, 3]
+        )
+        
+        return mcolors.to_rgba_array(color_array, converted_alphas)
 
     def get_facecolor(self):
         return self._maybe_depth_shade_and_sort_colors(super().get_facecolor())