diff --git a/lib/report/common/defaults.js b/lib/report/common/defaults.js
index fae736fe..a9851c32 100644
--- a/lib/report/common/defaults.js
+++ b/lib/report/common/defaults.js
@@ -24,12 +24,13 @@ module.exports = {
 
     colorize: function (str, clazz) {
         /* istanbul ignore if: untestable in batch mode */
-        if (supportsColor) {
-            var colors = {
-                low: '31;1',
-                medium: '33;1',
-                high: '32;1'
-            };
+        var colors = {
+            low: '31;1',
+            medium: '33;1',
+            high: '32;1'
+        };
+        
+        if (supportsColor && colors[clazz]) {
             return '\u001b[' + colors[clazz] + 'm' + str + '\u001b[0m';
         }
         return str;