A better way to create a Buff Leghorn that lays blue egg would be to mate a Buff leghorn rooster to a Cream Legbar pullet, breed the pullets back to Buff leghorn and from that point only breed the blue laying buff looking females, that is if somebody would want to create a buff leghorn that lays blue eggs, I see a market for themIf you back cross to pure Buff Leghorns enough generations you might get back to Buff Leghorns.This is usually done through the pure males until they are 15/16 Buff Leghorns.A long process and with this cross you have so many things to eliminate,slate legs,breards,blue egg shells,pea comb,red and dominant white.I would not bother,but scrap it and start over with pures.