this has got to be one of, if not THE hardest colors to come up with. Never, ever start from white (assuming you are working with b'cream). Instead, tint the icing a bright, bold pink or yellow or orange before adding any red gel/paste.
Then it will take much less and should not get that bitter taste many complain about.
IF you can tollerate (sp?) flavoring I recommend you add about 1/4 tsp UNsweetened KoolAid powder (per 1 cup of icing). (I have never actually measured how much KoolAid I add,) Any flavor that is red will work....personally I prefer black cherry. I've had people tell me strawberry has more color to it but I don't really think so
When using KoolAid it really needs some 8-12 hours for the color to develop so color the icing the night before. I ususally put it in the frig overnight, then the next morning you take it out.....there might be many black specks - which are undissolved KoolAid granuals -but don't panic.....just give it a good stir & they will disappear
One other hint: Helpful if you only need a small amount of icing - say up to 1/2 cup: Wilton puts out colored icing in tubes. There's about 2 oz in it for about $1.50. They are SOOOO color satuated you can scrape out the icing and add it to yours - even white - and it will still be red
I cut off the end of the tube to remove it.