Okay, so we are in the middle of the discussion about livestock/pet breeding. Breeding is the art of binding certain qualities together and creating a more or less uniform phenotype and stable genotype, so that every generation replicates the qualities you desire.
And the qualities you desire can be quite different from the qualities I wish to see in my birds. So, if you only want a bird that lays big eggs and makes a good table bird, than color is nothing you will breed for. You will breed the best laying hens to your biggest rooster and you will be okay with what ever the color the chicks will have, right? Or maybe you want to preserve the auto-sexing, too.
The auto-sexing color will get lost, if we only breed for eggs and meat. One white feather is not the end of the auto-sexing feature, but soon one feather multiplies into a bunch of white and .... you know what I mean.
Body shape, o/c you will breed for a body shape that is good for meat, but a good laying hen has a total different shape.. Look at the commercial hybirds. You can see form afar what type of hybird someone has, they are so different in shape. The dual purpose breeds try to find a compromise that helps the hen lay eggs and brings engouh bone (!) and muscle to support a big bird. A bird that still can walk and run and hopp around without all the cruel side effects for the life quality of the birds we see in commerical meat birds. Every dual purpose breed has found a different shape that supports the hens and brings good meat quality on/in the roosters. So you should breed to one of these shapes... and if you breed to one of these, why not breeding to the shape the Standard asks for?
In short: Breeding to the Standard will make it easier for you to produce the bird you want.
And if you miss some importent qualities in your birds, well. This is fine, too. That way the Australiens brought us the Australorps. Why not a Idafelder, a more heat tollerant Bielezona....?