Make Colormap() constructor permit base mcolors.Colormap

Author: lukelbd

proplot/colors.py

@@ -2290,6 +2290,8 @@ def __setitem__(self, key, item):
             item = ListedColormap(
                 item.colors, item.name, item.N
             )
+        elif isinstance(item, mcolors.Colormap):  # base class
+            pass
         else:
             raise ValueError(
                 f'Invalid colormap {item}. Must be instance of '

proplot/constructor.py

@@ -476,6 +476,8 @@ def _parse_modification(key, value):
             cmap = pcolors.ListedColormap(
                 arg.colors, arg.name, arg.N
             )
+        elif isinstance(arg, mcolors.Colormap):  # base class
+            cmap = arg
 
         # Dictionary of hue/sat/luminance values or 2-tuples
         elif isinstance(arg, dict):