diff --git a/color.php b/color.php
index 9777855..6692a91 100644
--- a/color.php
+++ b/color.php
@@ -254,7 +254,7 @@ class color
     $colorList = $color->colorList;
     if (! array_key_exists ($colorInText, $colorList))
       throw new \Exception (sprintf (dgettext ("domframework",
-                       "Unknown color provided to graphColor::textToRGB : %s"),
+                       "Unknown color provided to graphColor::textToRGB: '%s'"),
                        $colorInText), 500);
     return $colorList[$colorInText];
   }