Way back in the dark ages when I was a wee nipper, some evil corporate mastermind came up with the idea of repaints. Basically they said "I know, we can take this toy we already have, paint it a different colour, and sell it as a different toy!" And thus a marketing empire was born.
Possibly the most famous example of this are the Decepticon Seeker jets from Transformers.
Well, if a soulless toy campany can do it, so can I! I can now sell prints of one picture for the price of three!