See this Demo:
Why are we supporting hsb instead of hsl? Shouldn't we be supporting what is supported in css3? I have code that works, and has been in production use, if you're interested.
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I was hunting this one down. I've only narrowed it down to the Fx.CSS.Parsers.
Yeah the Fx.CSS.Parser.Color is lacking parsing of rgba values. Moving this to 1.5 for considerations.
We could use Color.js (currently at More) to manage (parsing and encoding) of the color. That should support hsl, hsb, rgb, rgba etc.