I patched up a spot in a smooth cast 300 replica I made. The fixit sculpt is a grey and the smooth cast a pure white. I was using a “wash” to color/paint the rack. Using oil colors mixed with lacquer thinner to stain/paint/wash the white rack to a normal color. Problem is that the gray fixit sculpt isn’t staining/painting like the rest of the rack. Any hints? Will I have to actually spray paint the fixit sculpt with white paint and then wash/stain it?