Sebright would bring in rose combs and henny feathered males. Traits that may pose a challenge to breed out. Not to mention neither Sebright nor Pekin have crests.
Designing a tolbunt colour from polish - Page 2
Did you look at my first response? If you could get hens with minimal competing traits with the right coloring, like Speckled Sussex, you could use actual Polish to start with. Since, you're breeding for a coloring that will take a few generations to get right, it doesn't really matter if you use a black or white Polish rooster to start with.