Canisters of cake frosting are not available in customised colours. If you want a deep maroon icing on your cake, for example, you must make it yourself. But you can't necessarily rely on the tiny squeeze bottles of food dye used to colour eggs; these are not strong enough to get the vivid, dark burgundy colour you need. While professional bakers use food colour gels for a more concentrated source of colour, there is more to colouring icing than just adding the gel and mixing.
Drop five drops of rose pink food colouring gel and one drop of violet food colouring gel into 2 cups of white icing. Stir the mixture with a spatula in order to evenly distribute the colour.
Check the colour. You can add five more drops of rose pink food colouring gel and one of violet food colouring gel if the mixture is too light for your liking. Stop adding colouring approximately one shade before it reaches the ideal darkness.
Cover the icing and let it sit for one hour. This period of rest allows the colours to fully develop and darken.
Mix in additional white icing if the maroon icing darkened too much during the one hour resting period. Conversely, you can add five parts of rose pink food colouring gel to one part violet food colouring gel to darken the icing even more.