Step 1: Your Arsenal
Liquid food colour is hopeless! You have to use way too much of it, then the taste of alcohol starts to take over and your icing will become way to runny. It can be okay to use in cake batters, jellies and rock candy but for vibrant buttercream it's just not good enough.
What you want to use is a concentrated gel. There are lots of brands out there and each have their own merit.
Here in Australia the most easily accessible is Queens which I buy from Woolworths. It comes in red, yellow, blue and green. Great by themselves but a little tedious to mix to get specific colours. They are a great base to start with though.
The most well known brand, I think, is Wilton. They come in a very extensive range of colours so they will suit almost any use you have for them. They come in a jar so are not convenient to use, and I find I have to use quite a lot of it.
I haven't tried this brand yet, but Chefmaster seems to be very highly spoken of. If you're familiar with it please let me know how it works for you.
My absolute favourite, the brand I use the most and have had the best results with is Americolor. They come in a squeeze bottle so they're very easy to use. The mix smoothly and blend very easily to make any colour you desire.
Step 2: Get a Toothbrush
Step 3: Just Put It Away
Make your frosting about three or four days in advance. Don't despair if it's not the colour you were hoping for. If it's only a few shades off, then perfect! Now wrap it up and stick it in the fridge.
When you're ready to use it take it out of the fridge, let it come to room temperature then give it a mix with your beaters. You will see the colour intensify right before your eyes!
Step 4: That's It
As always, please leave any questions, comments or suggestions. Happy creating :) \m/