In the 80's/90's, Do it Yourself/DIY cel kits were released for fans to paints themselves. The lines came preprinted onto acetate and you could buy the paints separately and apply the paint according to the color guide.
Pre-printed lineart of a Dororo (どろろ) DIY cel
Paint placement guide/instructions
Tips for painting your DIY cel
Princess Knight (リボンの騎士) DIY Cel
Candy Candy (キャンディ♡キャンディ) DIY Cel