Fix opacity for hidden legend item

c3.js

@@ -337,7 +337,7 @@
         };
 
         var isLegendRight = __legend_position === 'right';
-        var legendStep = 0, legendItemWidth = 0, legendItemHeight = 0;
+        var legendStep = 0, legendItemWidth = 0, legendItemHeight = 0, legendOpacityForHidden = 0.15;
 
         /*-- Define Functions --*/
 
@@ -3744,14 +3744,17 @@
         /*-- Draw Legend --*/
 
         function opacityForLegend(id) {
-            return d3.select(selectorLegend(id)).classed(CLASS.legendItemHidden) ? 0.5 : 1;
+            return d3.select(selectorLegend(id)).classed(CLASS.legendItemHidden) ? legendOpacityForHidden : 1;
+        }
+        function opacityForUnfocusedLegend(id) {
+            return d3.select(selectorLegend(id)).classed(CLASS.legendItemHidden) ? legendOpacityForHidden : 0.3;
         }
         function toggleFocusLegend(id, focus) {
             var legendItem = legend.selectAll('.' + CLASS.legendItem),
                 isTarget = function (d) { return (!id || d === id); },
                 notTarget = function (d) { return !isTarget(d); };
-            legendItem.filter(notTarget).transition().duration(100).style('opacity', focus ? 0.3 : opacityForLegend);
-            legendItem.filter(isTarget).transition().duration(100).style('opacity', focus ? opacityForLegend : 0.3);
+            legendItem.filter(notTarget).transition().duration(100).style('opacity', focus ? opacityForUnfocusedLegend : opacityForLegend);
+            legendItem.filter(isTarget).transition().duration(100).style('opacity', focus ? opacityForLegend : opacityForUnfocusedLegend);
         }
         function focusLegend(id) {
             toggleFocusLegend(id, true);
@@ -4044,7 +4047,7 @@
                 legend.selectAll(selectorLegends(targetIds))
                     .classed(CLASS.legendItemHidden, true)
                   .transition()
-                    .style('opacity', 0.5);
+                    .style('opacity', legendOpacityForHidden);
             }
 
             redraw({withUpdateOrgXDomain: true, withUpdateXDomain: true, withTransitionForHorizontalAxis: false});