Too much coloring can give your icing a nasty taste. I usually just add more white icing to the color. now if you have a really dark icing then it is best to start with a darker icing. I have taken my homemade icing and added a little bit of canned icing to it before adding coloring. Use the lemon for the yellows and oranges and greens. use the milk chocolate to a darker chocolate for deep red, blacks and browns. Be sure to test a small amount before making a big batch then realizing you messed up. Nothing is cheap now days so it is best to test first.