I used cooked sugar in my butter cream. The ratio of butter to sugar is much higher than in butter icing (where icing sugar is added into butter). Fondant and butter icing absorb and 'show' the red colorant better than buttercream due to the icing sugar content.. ..hope anyone who reads this would understand why, sometimes, the buttercream on the cake just dont look red enough...
I delivered a set of cupcakes this afternoon...was supposed to be red, but I guess, not red
but hey, look on the brighter side...at least you dont stuff so much colorant into your digestive system!