Solid outer colour cast

With this cast I have been trying to create a solid colour on the outside, and then for there to be coloured layers within the cast. My intention is to carve into the form once it is solid so as to reveal the colourful layers.

In order to create the solid colour on the outside, I pour the plaster into the bottom of the mould, and rotate the cast so as to coat all of the sides of the mould. When the mould is filled, I will pour a layer of plaster onto the top in the same colour as the plaster used on the sides of the mould.