DOC:added exported colors to colors.api

Author: 渡邉 美希

doc/api/colors_api.rst

@@ -71,3 +71,17 @@ Functions
    same_color
    get_named_colors_mapping
    make_norm_from_scale
+
+Exported colors
+---------------
+
+The data used to populate the :doc:`/gallery/color/named_colors` are exposed
+as dictionaries that map color names to hex strings.
+
+.. py:data:: BASE_COLORS
+
+.. py:data:: TABLEAU_COLORS
+
+.. py:data:: CSS4_COLORS
+
+.. py:data:: XKCD_COLORS