diff --git a/src/sugar/graphics/xocolor.py b/src/sugar/graphics/xocolor.py
index df609178..395e3454 100644
--- a/src/sugar/graphics/xocolor.py
+++ b/src/sugar/graphics/xocolor.py
@@ -209,6 +209,10 @@ colors = [
 
 
 def _parse_string(color_string):
+    if not isinstance(color_string, (str, unicode)):
+        logging.error('Invalid color string: %r', color_string)
+        return None
+
     if color_string == 'white':
         return ['#ffffff', '#414141']
     elif color_string == 'insensitive':