fix to_rgb_color_list when passing rgba colors (closes #3477)

Author: janosh

Diff for: packages/python/plotly/plotly/figure_factory/_annotated_heatmap.py

@@ -1,7 +1,7 @@
 from __future__ import absolute_import, division
 
-from plotly import exceptions, optional_imports
 import plotly.colors as clrs
+from plotly import exceptions, optional_imports
 from plotly.figure_factory import utils
 from plotly.graph_objs import graph_objs
 from plotly.validators.heatmap import ColorscaleValidator
@@ -147,9 +147,10 @@ def create_annotated_heatmap(
 
 
 def to_rgb_color_list(color_str, default):
-    if "rgb" in color_str:
-        return [int(v) for v in color_str.strip("rgb()").split(",")]
-    elif "#" in color_str:
+    color_str = color_str.strip()
+    if color_str.startswith("rgb"):
+        return [int(v) for v in color_str.strip("rgba()").split(",")]
+    elif color_str.startswith("#"):
         return clrs.hex_to_rgb(color_str)
     else:
         return default