Using hsl for colours has already been mentioned but here is the full explanation.  The hue is the distance around a full colour wheel (0 to 360). 

The saturation is the amount of that colour:

The lightness (or luminescence) is how bright the colour is.  This is achieved by adding equal amounts of the colours:

Using rgb might seem easier and gives the same results because hsl(0,100%,50%) is the same as rgb(75,31,31).  However, in rgb could you easily guess what colour would contrast nicely with that one?  In hsl you can as explained next.