to make purple you'll need pink and blue or magenta and blue. Red and blue results in a muddy purple color.
cant tell you the ratio but my guess would be roughly 3 parts pink and one part blue.
Do a test run to find out. You haven't even given us a brand of food coloring, and I doubt supermarket food coloring is precisely color matched even from one batch to the bext.
Also, keep in mind, purple is not actually the same thing as red plus blue. Depending on the absorption spectra of the dies, red plus blue could easily turn into muddy brown instead.
Thanks for the reply. Yeah it was more pink than blue