Block errors are highlighted in matching color.

- Upgrade to latest version of Snap
- Color math to tell Snap what color we want.

This is not really the end of this work. It demonstrates that
we have enough flexibility to do what we want. But we probably
still need to think about the error color palette in Pyret and
how it should work with the semantic color palette of the
Blocks world.

Author: asolove

src/web/js/output-ui.js

@@ -41,6 +41,14 @@
       return converter([74, a, b]);
     }
 
+    // Snap wants colors specified as "r,g,b(,a)" where each is [0-255]
+    var snapConverter = $.colorspaces.converter('CIELAB', 'sRGB')
+    function hueToSnapColor(hue) {
+      var a = 40*Math.cos(hue);
+      var b = 40*Math.sin(hue)
+      return snapConverter([74, a, b]).map(x => Math.floor(x * 255)).join(",")
+    }
+
     var goldenAngle = 2.39996322972865332;
     var lastHue = 0;
 
@@ -1079,9 +1087,12 @@
                   // Blocks editor case
                   if(CPO.blocksIDE) {
                     if(positions.length > 0) {
+                      var snapColor = hueToSnapColor(color);
                       CPO.blocksIDE.flashSpriteScripts(
                         positions[0].from.line + 1, // CPO is 0-based, Snap is 1-based
-                        positions[0].to.line + 1);
+                        positions[0].to.line + 1,
+                        undefined,
+                        snapColor);
                     }
                   } else {
                     if (positions[0] !== undefined)