To add color, paste works better than liquid in my opinion. I have found a taste free paste that I really like to use. I get it at Michael's and it says taste free on the bottle.
Ingredients
4cupsPowdered Sugar
1/4cupCorn SyrupAdds shine
1tsp. Vanilla
Pinch of salt
Food Coloring to tint
Instructions
In a large bowl mix all ingredients until smooth. Add paste food coloring to tint.