hsl(...) / hsla(...). Saturation and lightness are CSS percentages (0..100), hue is degrees (any double; normalized modulo 360 during conversion).
hsl(...)
hsla(...)
Alpha channel, 0..255 (255 = opaque).
0..255
255
Blue channel, 0..255.
Green channel, 0..255.
Red channel, 0..255.
Canonical CSS string form for this color (e.g. #ff8800, rgba(255, 0, 0, 0.5)).
#ff8800
rgba(255, 0, 0, 0.5)