I really like carbon because I know when to quit sanding, on the other hand sanding silkspan is tough.. I can't tell when I've gone too far until I put a coat of dope on and discover raw wood.. What would it hurt to put a coat of color on before you started the fill coats.. When you get to the color dope you know you are into the silkspan..

I've tried putting a little color in the filler but it really didn't help all that much..