Just RGB, and a fairly baroque interface, but it works.
c-r, r, 8, g, 1, b, 1 gets the colour you see in the screenshot.
q to exit colour selection (actually you can select tools and that seems to work OK).
t-p to draw with the colour using the pen.
Writing this (2.5 hours) reveals that the keymap interface needs rationalising. As in “making rational”. 🙂