Oky this is were the bias bit comes out. 0_o
Feser i have nothing against them and we have never had a issue with the full blown coolants (they dyes to me are weak). Under testing there coolants do work and ive never managed to make them fall out, how ever there are other coolants out there that in the past "have" fallen out or faded quickly under our testing how ever im not here to name them.
Food colouring is not made to last and is not the best dye to use how ever some of it is very good. In the UK supermarkets food colouring contain more than just sugar and if you would like to gum up your system then carry on how ever its not some thing we advise. If you going to experiment as we do then pure colourants are much better. If you going to use food colourants then name the product E Number as there are hundreds of different ones out there and some are rubbish and some are good and some well just forget it. You can also look at laser dyes
When choosing a dye and experimenting try to get the purest one you can and try to get it from a reputable place. Dyes are not just dyes they are all so packed out with many other chemicals, Pure dyes are extremely expensive. All ways check MSDS sheets and do a little re-search before just jumping head first into the fire.
Above all have fun. Do what you think is best and if it doesn't work try some thing different.