Fix bug ZK-1693: Dial chart customize color issues
http://tracker.zkoss.org/browse/ZK-1693
Fix bug ZK-1692: widget.isVisible API doesn't work properly
http://tracker.zkoss.org/browse/ZK-1692
Merge remote-tracking branch 'VincentJian/B65-ZK-1692'
Re-fix bug ZK-1692