Add block documentation

docs/_data/variables/form/tools.json

@@ -20,12 +20,18 @@
       "type": "variable",
       "computed_type": "size",
       "computed_value": "0.75rem"
+    },
+    "$label-colors": {
+      "name": "$label-colors",
+      "value": "$form-colors",
+      "type": "variable"
     }
   },
   "list": [
     "$label-color",
     "$label-weight",
-    "$help-size"
+    "$help-size",
+    "$label-colors"
   ],
   "file_path": "form/tools.sass"
 }