Hey BenjiisMummy. I am a Cake decorator and would like to let you know that it is possible to get black icing. You just need the right product. If you go to a cake decorating supplies shop in your state they will sell colour gels or concentrated colours. One brand is Wilton but there are others as well. They are the best and come in many colours. Liquid colour will never go any darker then dark grey as mentioned above.
I have learnt from experience that it is hard to get buttercream to go black. It ends up an ugly shade of very dark green for some reason. But Royal or Ready to Roll (Orchard) Icing will go black for you. Goodluck.