When using store bought make up to blush your clay sculpt, apply lightly in layers to achieve the color you want.
Then with a stiff brush lightly pounce the color into the wet clay.
(I only use polymer clays for this, I don't know how it works with other kinds of clay.)
Then use a soft conditioned paint brush to smooth the clay, or leave it for a textured look.
When baked the makeup will lose some of it's original color but will be baked into the clay and is permanent.