Add opacity support for colorscale interpolation

Author: mdtusz

src/components/colorscale/make_scale_function.js

@@ -26,18 +26,20 @@ module.exports = function makeScaleFunction(scl, cmin, cmax) {
     for(var i = 0; i < N; i++) {
         si = scl[i];
         domain[i] = cmin + si[0] * (cmax - cmin);
-        range[i] = si[1];
+        range[i] = tinycolor(si[1]).toRgb();
     }
 
     var sclFunc = d3.scale.linear()
         .domain(domain)
-        .interpolate(d3.interpolateRgb)
+        .interpolate(d3.interpolateObject)
         .range(range);
 
     return function(v) {
         if(isNumeric(v)) {
-            var sclVal = Lib.constrain(v, cmin, cmax);
-            return sclFunc(sclVal);
+            var sclVal = Lib.constrain(v, cmin, cmax),
+                colorObj = sclFunc(sclVal);
+
+            return tinycolor(colorObj).toRgbString();
         }
         else if(tinycolor(v).isValid()) return v;
         else return Color.defaultLine;