1. #rrggbbaa hex color notation

    The CSS Color Module Level 4 defines new 4 & 8 character hex notation for color to include the opacity level.

  2. CSS3 Colors

    Method of describing colors using Hue, Saturation and Lightness (hsl()) rather than just RGB, as well as allowing alpha-transparency with rgba() and hsla().

  3. types: <color>: alpha color values (`rgba()`, `hsla()`)

  4. types: <color>: rgba hexadecimal notation (`#rrggbbaa`, `#rgba`)

  5. types: <color>: allow floats in `rgb()` and `rgba()`