The amount of white on barred breeds is not fixed (lot of variation), I've heard that some strains of BR can be color sexed at hatch, but for most I think it's unreliable. Once their wing feathers start growing in, that is a far better indication as the male's feathers have white stripes that are about twice as wide as the females. If you look at a whole group of straight-run chicks, the males pop out visually as much lighter in color. This effect starts in just a few days, but gets increasingly prominent as the wing feathers grow longer. At about 2 weeks, it's very obvious. Black barred chickens are not considered to be "auto sexing" because this effect is not reliable at hatch time, and also the effect is a matter of degree, unless you are very experienced, you need to compare a bunch of chicks and hope you can sort of the sexes.
As a rule this applies equally to any black barred chicken, so the same effect is seen on Dominiques, Barred Hollands, California Greys, and the various "cuckoo" colors like Marans.
Barred brown (with wild type down coloring, i.e. "chipmunk stripe" chicks) chickens are a mixed bag, if they have certain other genes, it hides the white spot on their head, but if those genes are not present, you get autosexing chicks, to various degrees. Examples of this are Rhodebars, Legbars, and Norwegion Jaehons (so I've read, never had these). In true autosexing breeds, anyone can see the difference, it's as if they are entirely different breeds, no comparison or "trained eye" is needed.
Edited by SilkieSensation - 3/7/15 at 3:20am