Hover over the square to change saturation (left to right) and value (bottom to top) of the last hue.

Use the keyboard to rotate hue:
j rotates slowly counterclockwise,
k rotates quickly clockwise, and
l rotates slowly clockwise.

Jump to a primary or secondary color: red, green, blue, cyan, magenta, or yellow. The enter key will also add the current color to the pick list.