Sex linked coloration is what you are after, I suspect. Usually, the male chick in the more common Barred Rock - f sexlink pairings has a white feathered spot on its head at hatching.
"The barring characteristic in BPR's is transmitted from the dam to the son... It is when BPR females are mated to RIR, NHR or WW males that the plumage and down differs. When BPR males are mated to RIR, NHR or WW females, the sexes cannot be distingusihed at hatching."**
Unless your birds are sex-links, the markings on a pure Barred Rock chick are going to be iffy to the inexperienced. The link for Dominiques offers hope, but the markings can run the gamut of variation. There seems to be little that is concrete, across the board.
After 13 days, your best course is to wait - you'll know in a few months which is which.
** Morley A. Jull, "Successful Poultry Management," 1943