After a consultation with my resident rainbow expert, I have added green to the mix. I think she knows what shes talking about. I have also included a faux screenprint version in the image on the right, in an attempt to make the piece look as realistic as possible. I replaced the cyan and magenta channels in the texture with dot-screened versions (with the appropriate screen angles) to get this effect. It looks OK, but Im not sold... yet.
ROY and I are good friends :) I looked at using all 7 primary colors in the rainbow, but four looks better from a design perspective. Now its finding a color palette that works. Ill probably adjust itonce the entire illustration is assembled.