Definitely interesting.
When I look up the Diamond Duchess online, I do not see crests on them. So if your chicks do grow crests, they are something different.
Even hatchery Barred Rocks should have males lighter than females, because it is an unavoidable effect of the way the barring gene works. If the entire flock is barred, and all chicks show barring, then males will be lighter. This is because male birds have sex chromosomes ZZ, with barring being on the Z chromosome, so roosters have two barring genes. Females have ZW, with barring only on the Z, so females have just one barring gene. Two barring genes cause the bird to be lighter than one barring gene. The only way to get darker males is for them to have one barring gene and one not-barred gene, but in that case the flock would also be producing some chicks with no barring at all (female with a not-barred gene, or male with two not-barred genes.)
When male and female chicks have just one barring gene, so they look equally dark, it is generally because they have a barred father (and he gave one barring gene to each chick) and a not-barred mother (who gave a not-barred gene to her sons and a W chromosome to her daughters, so each sex still has just the one barring gene they got from their mother.)
So I would suspect a cross of Cream Legbar father (barring gene and crest on the head) with some other kind of hen (not barred). If Cream Legbar is involved, they will probably lay blue or green eggs.
