The scifi zamboony has a colorize overlay. But it's grey tones were underlaid. I like the process of working with the line art that has been filled and alised to alpha. Much better than multiplying the line art into color .
I took a super, loose, small , thumbnail and blew it up and used this underlay idea. But I'm also working from color photos for my color picks. These colors were from a shot of vacation cabins in Tahiti. That dodges my whole color blind issue. Picking darkest darks, lightest lights right from a photo. Also, using the Candice channel technique, I advise duplicating the single GRAY channel while in grayscale vs duplicating the blue channel while in RGB mode. Then switch to rgb . The selection channel will travel with the mode change.