Make displacy color registry consistent with others

This was the only registry that expected the registered objects to be dictionaries instead of functions that return something. We can still support plain dicts but we should also support functions for consistency

spacy/displacy/render.py

@@ -249,6 +249,12 @@ class EntityRenderer:
         colors = dict(DEFAULT_LABEL_COLORS)
         user_colors = registry.displacy_colors.get_all()
         for user_color in user_colors.values():
+            if callable(user_color):
+                # Since this comes from the function registry, we want to make
+                # sure we support functions that *return* a dict of colors
+                user_color = user_color()
+            if not isinstance(user_color, dict):
+                raise ValueError(Errors.E925.format(obj=type(user_color)))
             colors.update(user_color)
         colors.update(options.get("colors", {}))
         self.default_color = DEFAULT_ENTITY_COLOR

spacy/errors.py

@@ -476,6 +476,8 @@ class Errors:
     E199 = ("Unable to merge 0-length span at doc[{start}:{end}].")
 
     # TODO: fix numbering after merging develop into master
+    E925 = ("Invalid color values for displaCy visualizer: expected dictionary "
+            "mapping label names to colors but got: {obj}")
     E926 = ("It looks like you're trying to modify nlp.{attr} directly. This "
             "doesn't work because it's an immutable computed property. If you "
             "need to modify the pipeline, use the built-in methods like "