Red and blue make purple, just start with the blue and slowly add some red.
I have at times just used a 1/2 container of violet. Also there is a gel neon purple that I picked up at walmart that has been close to barney color. It is not wilton, is in the bakery section with the cake mixes.
Thanks (minorfan) I'll have to try and look for the neon color. Hopefully they'll have it.
AmeriColor Electric Purple