From 15817e78a162be95870e28df62091f2345202acb Mon Sep 17 00:00:00 2001
From: Andrew n marshall <Anm@anm.me>
Date: Thu, 31 May 2018 12:31:18 -0700
Subject: [PATCH] Fix case where lack of colour attribute results in null.
 (#1894)

Fixes regression in #1893. Patch on change in #1831.
Verify typeof colour variable before passing through Number().
Missing attributes return null, and Number(null) === 0, resulting in a red hues category color.
---
 core/toolbox.js | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/core/toolbox.js b/core/toolbox.js
index a0e692a2d..359fec8bb 100644
--- a/core/toolbox.js
+++ b/core/toolbox.js
@@ -334,10 +334,14 @@ Blockly.Toolbox.prototype.syncTrees_ = function(treeIn, treeOut, pathToMedia) {
         // (eg. `%{BKY_MATH_HUE}`).
         var colour = Blockly.utils.replaceMessageReferences(
             childIn.getAttribute('colour'));
-        if (/^#[0-9a-fA-F]{6}$/.test(colour)) {
+        if (colour === null || colour === '') {
+          // No attribute. No colour.
+          childOut.hexColour = '';
+        } else if (/^#[0-9a-fA-F]{6}$/.test(colour)) {
           childOut.hexColour = colour;
           this.hasColours_ = true;
-        } else if (!isNaN(Number(colour))) {
+        } else if (typeof colour === 'number'
+            || (typeof colour === 'string' && !isNaN(Number(colour)))) {
           childOut.hexColour = Blockly.hueToRgb(Number(colour));
           this.hasColours_ = true;
         } else {