Fix intersectionColor in conic cone visualizer.

Originally reported here: https://groups.google.com/d/msg/cesium-dev/WZkKLcnMjUY/evGdLCwY5bQJ
Changes after review.
Remove useless parameter.
Merge pull request #979 from AnalyticalGraphicsInc/cone-visualizer-intersectionColor

Fix intersectionColor in conic cone visualizer.