The model makes monochromatic art without having to use trigger words but will occasionally add hints of color here and there. The model also has a more difficult time making monochromatic images of male subjects. If you are having trouble getting the results you want, try adding one or more of these prompts: monochrome, line art, sketch, and coloring page. This tends to help.
use prompts monochrome, line art, b&w, coloring page
