New rule: similar colors

lib/metadata/policies.js

@@ -463,7 +463,7 @@ var policies = {
     },
     "cssColors": {
         "tool": "phantomas",
-        "label": "Different colors",
+        "label": "Colors count",
         "message": "<p>This is the number of different colors defined in CSS.</p><p>Your CSS project will be easier to maintain if you keep a small color set.</p>",
         "isOkThreshold": 30,
         "isBadThreshold": 150,
@@ -507,6 +507,21 @@ var policies = {
             };
         }
     },
+    "similarColors": {
+        "tool": "colorDiff",
+        "label": "Similar colors",
+        "message": "<p>This is the list of colors found in the stylesheets, that are very close to each other. The eye can barely see the difference.</p><p>Use this list to reduce the number of colors in your palette, it will be easier to maintain.</p>",
+        "isOkThreshold": 0,
+        "isBadThreshold": 40,
+        "isAbnormalThreshold": 80,
+        "hasOffenders": true,
+        "offendersTransformFn": function(offenders) {
+            return {
+                count: offenders.length,
+                list: offenders
+            };
+        }
+    },
     "cssImports": {
         "tool": "phantomas",
         "label": "Uses of @import",
@@ -970,7 +985,7 @@ var policies = {
         "tool": "phantomas",
         "label": "Hidden images",
         "message": "<p>List of all images that have a display:none property, or one of their parents. These images are loaded by the browser even if they're not visible. You might be able to find a way to lazy-load them, only when they get visible.</p><p>Trackers are an exception, you'd better hide them.</p>",
-        "isOkThreshold": 3,
+        "isOkThreshold": 1,
         "isBadThreshold": 12,
         "isAbnormalThreshold": 30,
         "hasOffenders": true

lib/metadata/scoreProfileGeneric.json

@@ -70,7 +70,8 @@
                 "cssRules": 2,
                 "cssComplexSelectors": 2,
                 "cssComplexSelectorsByAttribute": 1.5,
-                "cssColors": 0.5
+                "cssColors": 0.5,
+                "similarColors": 0.5
             }
         },
         "badCSS": {