I just do a thin coating of the icing I'm going to use to ice the cake
In my case its always butter icing which my recipe is 200g butter 200g icing sugar (or 250x250) and 1 tsp vanilla. Beat/Mix the butter till its pale, add the vanilla and sugar, Mix again till light and desired consistency. Then just divide up into however many bowls you need for whatever colours you want
But generally the buttercoating is non coloured for the crumb coating iykwim?