4096 Color Wheel Version 2.1 by Jemima Pereira. Free for any use. 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.