8 digit hex codes
Hey awesome thing you've got here! 

What do you think about 8 digit hex codes, as explained [here](https://css-tricks.com/8-digit-hex-codes/)? The rightmost 2 digits represent alpha value.

I know apps like Photoshop don't use them, so maybe they'd only be implemented for the pickers that do use them. I know Chrome does.

I'd be happy to PR, but if you are rethinking color conversions for v3, maybe this is something that should be done on the color conversion library level? Let me know if you have any thoughts!