Once dry a thinner mix of royal icing is "flooded" in to each section. (the thinner mix is made by adding egg white to a normal mix of icing sugar very slowly, to avoid adding bubbles. The mix should be so thin that when poured it will flow out level, or "flood" the area it is piped in to.
When using such strong colours you need to add each section of colour one at a time and allow to dry or the colours will run in to each other