Citadel Corax White Primer Spray Citadel Colour spray cans are designed for undercoating metal and plastic models. The purpose of the undercoat is twofold: it acts as a primer and it provides a flat base colour to paint onto. You will find that a spray finish is far flatter and better to paint onto than a brushed undercoat. This can contains 400ml of black undercoat. Age 16+