I'm surprised the practice of breeding white ones with each other producing more white ones and then dying them different colours hasn't taken off.
It would be easily possible as being white they wouldn't need any undercoat/primer or anything, and you can surely get dye that isn't harmful to their skin and will last. You might have to get it renewed each year if they fade.
Potential business opportunity, actually. I can see it becoming next year's 'must have'.