I have not been albe to make purple, in anything, fondant, buttercream even gumpaste ??? I use Wiltons violet and Americolours violet, purple, electric purple and even airbrush purple sheen. All either never go purple or quickly turn blue as it dries. What do you use ? I see so many beautiful creations with lovely shades of purple. I need to know, please HELP
Are your base materials homemade with local tap water?
Do you have an RO water softener unit in your house?
Try using distilled water to avoid minerals that cause colour changes. Or use milk or cream. Once your base is dry, there should be no reason that the spray would turn colour.
For gumpaste, try a recipe that uses only eggwhite (it's safe to eat after it has dried completely). Avoid cream of tartar or juice or acid of any kind.
I have no trouble making purple icing with the cooked milk+flour recipe using Nielson's milk and crisco.
You can also try the powdered Crystal Colors, they don't change color. I brush purple on gumpaste, I don't try to put it into the gumpaste itself. If it's just on the surface it doesn't change color. Purple is tricky, though, it can mess you up... http://acaketorememberva.blogspot.com/2011/09/purple-oh-how-i-hate-you.html