Document color formats

[talaj]

In addition to the list of supported color literals also other color formats should be documented. Or at least state that the format is the same as in CSS.

These formats are supported:

• #FFFFFF
• #FFFFFFFF
• rgb(255, 255, 255)
• rgba(255, 255, 255, 1.0)
• rgb(100%, 100%, 100%)
• rgba(100%, 100%, 100%, 1.0)
• hsl(360, 100%, 100%)
• hsla(360, 100%, 100%, 1.0)