Here in the UK they have Royal Icing Mix that you just need to add water to. I'm planning on making black royal icing for some sugar cookies tomorrow, but what's the best way to make my royal icing black? Should I add some cocoa powder to the mix and then black coloring? If I do, will the cocoa change the consistancy of the pre made icing mix? (I've used the mix before, and it worked just fine when I made a gingerbread house from it)
I've made black RI by adding cocoa first, then black color. It will make your RI a little thicker, just add some more water, small amounts at a time.