HSL
A way of writing a screen colour as hue, saturation and lightness instead of red, green and blue.
Also: hue saturation lightness
HSL rearranges RGB into terms that are easier for people to think in. Hue is an angle on the colour wheel from 0 to 360 degrees, with red at 0, green at 120 and blue at 240. Saturation runs from 0 per cent, grey, to 100 per cent, vivid. Lightness runs from 0, black, through the pure colour at 50, to 100, white. It is handy for making lighter and darker versions of a colour. Its weakness is that equal lightness numbers do not look equally light: yellow at 50 looks far brighter than blue at 50.