Guys, check this thread
for more information about the icons, I will get the documentation updated since it is listing just how to set a background image for the icon. The default icons are specified with -webkit-mask-box-image (and dataURI, but this is not mandatory) and are PNG-8/24 images with alpha transparency. Since PNG-8 with alpha can be only made with Adobe Fireworks or a special commercial plugin for Photoshop, I would recommend using PNG-24. The transparency level defines the mask (icon), so the non-transparent areas will get colorized and vice versa.
@Saurabh: Your PNG image is not transparent and using the above method will be rendered as a colorized square.
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