Oof... hopefully u haven't spent too much time on this because it's futile.. the breeding system in this game is actually pretty simplistic since it's based on presets instead of genetic or rng-based generation. So if u see no pink oni existing already, u won't be able to make one since it means there's no preset for it.I am not too sure how to breed the color I want and I don't seem to be able to rng it.
Try 'Slave Matrix' if u're looking for a suprisingly complex breeding mechanic (and yes, it's a finished game)