diff --git a/core/block.js b/core/block.js
index 07fa108c4..f62419231 100644
--- a/core/block.js
+++ b/core/block.js
@@ -1361,6 +1361,13 @@ Blockly.Block.prototype.jsonInit = function(json) {
   }
 
   // Set basic properties of block.
+  // Makes styles backward compatible with old way of defining hat style.
+  if (json['style'] && json['style'].hat) {
+    this.hat = json['style'].hat;
+    //Must set to null so it doesn't error when checking for style and colour.
+    json['style'] = null;
+  }
+
   if (json['style'] && json['colour']) {
     throw Error(warningPrefix + 'Must not have both a colour and a style.');
   } else if (json['style']) {
diff --git a/core/block_render_svg.js b/core/block_render_svg.js
index 2cff473c7..c530f6061 100644
--- a/core/block_render_svg.js
+++ b/core/block_render_svg.js
@@ -566,7 +566,7 @@ Blockly.BlockSvg.prototype.renderDraw_ = function(iconWidth, inputRows) {
       if (prevBlock && prevBlock.getNextBlock() == this) {
         this.squareTopLeftCorner_ = true;
       }
-    } else if (Blockly.BlockSvg.START_HAT || this.hat) {
+    } else if (Blockly.BlockSvg.START_HAT || this.hat === 'cap') {
       // No output or previous connection.
       this.squareTopLeftCorner_ = true;
       this.startHat_ = true;
diff --git a/core/blockly.js b/core/blockly.js
index fcfa0b95d..4f120e4d5 100644
--- a/core/blockly.js
+++ b/core/blockly.js
@@ -689,8 +689,12 @@ Blockly.setTheme = function(theme) {
   this.theme_ = theme;
   var ws = Blockly.getMainWorkspace();
 
-  //update blocks in workspace
-  this.updateBlockStyles_(ws.getAllBlocks());
+  //update all blocks in workspace that have a style name
+  this.updateBlockStyles_(ws.getAllBlocks().filter(
+      function(block){
+        return block.getStyleName() !== undefined;
+      }
+  ));
 
   //update blocks in the flyout
   if (!ws.toolbox_ && ws.flyout_ && ws.flyout_.workspace_) {
diff --git a/tests/blocks/test_blocks.js b/tests/blocks/test_blocks.js
index 3a092309d..f7a00062e 100644
--- a/tests/blocks/test_blocks.js
+++ b/tests/blocks/test_blocks.js
@@ -30,7 +30,7 @@ Blockly.defineBlocksWithJsonArray([  // BEGIN JSON EXTRACT
     "message0": "value to stack",
     "nextStatement": null,
     "output": null,
-    "colour": 230
+    "style": "math_blocks"
   },
   {
     "type": "value_to_statement",
@@ -42,7 +42,7 @@ Blockly.defineBlocksWithJsonArray([  // BEGIN JSON EXTRACT
       }
     ],
     "output": null,
-    "colour": 230
+    "style": "math_blocks"
   },
   {
     "type": "limit_instances",
@@ -58,7 +58,7 @@ Blockly.defineBlocksWithJsonArray([  // BEGIN JSON EXTRACT
     ],
     "previousStatement": null,
     "nextStatement": null,
-    "colour": 230,
+    "style": "math_blocks",
   },
   {
     "type": "example_dropdown_long",
@@ -199,7 +199,7 @@ Blockly.defineBlocksWithJsonArray([  // BEGIN JSON EXTRACT
         "text": "0"
       }
     ],
-    "colour": 230,
+    "style": "math_blocks",
     "output": "Number",
     "tooltip": "A number."
   },
@@ -214,7 +214,7 @@ Blockly.defineBlocksWithJsonArray([  // BEGIN JSON EXTRACT
         "text": "0"
       }
     ],
-    "colour": 230,
+    "style": "math_blocks",
     "output": "Number",
     "tooltip": "An integer."
   },
@@ -229,7 +229,7 @@ Blockly.defineBlocksWithJsonArray([  // BEGIN JSON EXTRACT
         "text": "0"
       }
     ],
-    "colour": 230,
+    "style": "math_blocks",
     "output": "Number",
     "tooltip": "A dollar amount."
   },
@@ -246,7 +246,7 @@ Blockly.defineBlocksWithJsonArray([  // BEGIN JSON EXTRACT
         "text": "0"
       }
     ],
-    "colour": 230,
+    "style": "math_blocks",
     "output": "Note",
     "tooltip": "A midi note."
   },
@@ -262,7 +262,7 @@ Blockly.defineBlocksWithJsonArray([  // BEGIN JSON EXTRACT
         "alt": "*"
       }
     ],
-    "colour": 160
+    "style": "text_blocks"
   },
   {
     "type": "image_small",
@@ -276,7 +276,7 @@ Blockly.defineBlocksWithJsonArray([  // BEGIN JSON EXTRACT
         "alt": "*"
       }
     ],
-    "colour": 160
+    "style": "text_blocks"
   },
   {
     "type": "image_large",
@@ -290,7 +290,7 @@ Blockly.defineBlocksWithJsonArray([  // BEGIN JSON EXTRACT
         "alt": "*"
       }
     ],
-    "colour": 160
+    "style": "text_blocks"
   },
   {
     "type": "image_missing",
@@ -304,7 +304,7 @@ Blockly.defineBlocksWithJsonArray([  // BEGIN JSON EXTRACT
         "alt": "*"
       }
     ],
-    "colour": 160
+    "style": "text_blocks"
   },
   {
     "type": "test_with_lots_of_network_icons",
@@ -429,7 +429,7 @@ Blockly.defineBlocksWithJsonArray([  // BEGIN JSON EXTRACT
         "alt": "H"
       }
     ],
-    "colour": 160
+    "style": "text_blocks"
   },
   {
     "type": "styled_event_cap",