rainbow florist designs

What kind of dye they use to make rainbow roses? There can be as simple as food coloring right?
I saw the rainbow Roses "in any part of the network and I can not help wondering how they develop. Unfortunately, not sold, or even by boat, these flowers where I am located then I thought make some. The problem is that I do not know how. Initially, I thought the food coloring and celery experiment we have every primary school but can not be so simple like that. The florist who designed this particular building in the Netherlands is only to say that is a type of natural dye used. No help is appreciated.
It is not food coloring, but it is a natural plant dye. The producer was very protective of roses in their manufacturing process. So far, nobody understood the process of how he created the roses. The best thing to do for you is the same as everyone tries to solve it. Just experiment and see what happens.