The HSL and HSV color spaces are simple geometric transformations of the RGB cube into cylindrical form. The outer top circle of the HSV cylinder – or the outer middle circle of the HSL cylinder – can be thought of as a color wheel. There is no authoritative way of labelling the colors in such a color wheel, but the six colors which fall at the corners of the RGB cube are given names in the X11 color list, and are named keywords in HTML.