RGBA (Red, Green, Blue, Alpha-Opacity)
HSL (Hue, Saturation, Lightness)
HSLA (Hue, Saturation, Lightness, Alpha-Opacity)
Resumindo:
- Existiam RGB, Hexadecimal e Nomes de Cores. Com o CSS3, passamos a ter: RGB, Hexadecimal, Nomes de Cores (com novos), RGBA, HSL, HSLA.
Fonte:
"CSS3 brings with it support for some new ways of describing colours . Prior to CSS3, we almost always declared colours using the hexadecimal format (#FFF, or #FFFFFF for white). It was also possible to declare colours using the rgb() notation, providing either integers (0–255) or percentages.
The color keywork list has been extended in the to include 147 additional keyword colors (that are generally well supported), CSS3 also provides us with a number of other options: HSL, HSLA, and RGBA. The most notable change with these new color types is the ability to declare semitransparent colors."
https://medium.com/beginners-guide-to-mobile-web-development/whats-new-in-css-3-dcd7fa6122e1