The image color normally cycles around the entire hue wheel, at the speed and direction dictated by the Color Speed parameter. In Loop Hue mode, cycling is limited to a subset of the hue wheel. The size of the subset is determined by Hue Loop Length. Loop Hue affects new rings only; existing rings are unaffected.
Enabling Loop Hue causes the hue to immediately reverse direction: the current hue becomes one end of the loop, and the loop length determines the other end. For example, suppose the hue is currently 240° (blue), Color Speed is positive (clockwise), and the loop length is 60°. In this case, enabling Loop Hue causes the hue to cycle counterclockwise until it reaches 180° (cyan), at which point it reverses direction again and heads back towards blue.
A hue loop can be moved around the hue wheel, using the mouse or the Rotate Hue command. Manual hue changes are more dramatic when cycling is limited; 360° cycling tends to upstage them.