Coloring icing is very easy to do with all of the food safe colors on the market today. There is basically every color you can imagine available in food dye. However it would be costly to buy all of them for the possibly of using them one day. I recommend buying the colors you need now and than mixing 2 or more colors to get the ones you do not have when you need them. Color mixing can be difficult to do, so I would start with mixing a small amount of color at a time. This way you will gradually see if you are achieving the color you need.