My Barred Rock lays a lighter colored brown egg than the Buff Orp. It's not really pink, but a light beige. The BR's egg is also heavier. If you weigh the eggs, her's is a 2oz -2.2oz. The BO is generally 1.8oz.
I noticed that Blue-Kote doesn't dry very quickly, so I sprayed one girls bum lightly with it... her egg was streaked blue. Doesn't make for a pretty egg, but it works!
I built trapnests for mine. I haven't started using them yet, but I will when I have more than one or two girls in my breeder pens where I can't tell them apart. I can tell the silkie eggs apart, and even the Mille Fleurs, but my Dorkings all look identical.