The Colour Shift brush C doesn’t paint a colour of its own—it nudges whatever you paint over to the next colour along a ramp in your palette. It’s a fast way to add shading and highlights while staying strictly on-palette.
The ramp is defined by your primary and secondary colours:
Set the primary colour to the first colour of the ramp. Palette colours before it are never affected.
Set the secondary colour to the last colour of the ramp. The distance between the two sets the ramp width.
From the primary onward, the palette is treated as a run of consecutive ramps of that width. A painted pixel shifts only within its own ramp—it stops at the ramp’s end rather than spilling into the next one. That means one primary/secondary pair can drive several same-width ramps at once (for example, a palette laid out as rows of 4 shades per hue).
Brush size, shape, and symmetry all apply.