Omalley
Master

I tried to dye one of the plants from the enchanted wheelbarrow, with a Zento Orchid dye (Cooking BOD Reward) and I get the error message, "You Can Not Dye That" other Natural Dyes work fine. The Zenton Orchid dye is considered a "Natural" dye.
Source: https://uo.com/wiki/ultima-online-wiki/items/seasonal-promotional-items/

My guess is the Umbran Violet, and the dyes from Alchemy Bod Rewards will do the same thing.. but I have no proof on that, as i have no way to test it.