I have tried the liquid and the paste forms of the food dyes. The paste form takes quite a bit more tinkering than the liquid form due to the additives there to form the paste. I used the word paste, but 'gel' is probably more applicable here.
They both work though.
Erythrosine is a food dye. That is why I use it. It is the least toxic and expensive of all of the dyes for use in experiments of any sort requiring a good dye.