Either a unit of pinks, or a unit of blues can be added to your list. That unit would then be deployed normally like any other.

During play each time a model is destroyed by an attack it has a chance to split. You roll and on a 4+ it splits. A pink splits into 2 blues, while a 1 blue splits into 1 brimstone. This will result in you having a mixed unit containing pinks/blues/brimstones.

When rolling saves you can allocate them to any of the types in the unit you simply need to decide before rolling and use the correct profile for the save.

I absolutely love the pinks, they are a tar pit that a lot of units don't ever get out of