Gel colouring goes a long way. Use toothpicks dipped into the gel to get a small amount. Build colours by adding a little bit of gel at a time.
The initial coat of icing is called the crumb coat (because it keeps little bits of cake from marring the finished surface). Chilling the cake after the crumb coat makes it much easier to spread on ombré icing and ensures a beautiful finished cake. (See our how-to video).