You can use this Sugarflair Pastel Spectral Dark Brown Food Colouring Paste to colour any type of icing from sugarpastes and royal icing to buttercream and cake mixes.
Use sparingly to achieve a pastel shade to begin with and then gradually add more to give you a stronger more vibrant colour. This shouldn't change the consistency of your mixture too much.
You can also use it to paint on to decorations - if you choose to do this, we recommend you dilute the paste with a little rejuvinator spirit or clear spirit. You can use water but it won't give such a good finish.