Currently the shading ink mode lets you adjust pixels “left” or “right” along the selected strip of colors. When a pixel reaches the leftmost or rightmost extreme (so, normally, brightest or darkest) it stops there, and futher painting just saturates against the limit.
For some palette cycling effects, it would be useful to be able to have values wrap instead. In particular, think of a color range that is a hue cycle or rainbow. So if your color strip was:
[ red, yellow, green, blue, purple ]
Pushing pixels right along the strip from purple would color them red, and left from red would be purple.