I have noticed, at least with my partridges, that most of them can be feather sexed when their adult plumage starts coming in. The males get vibrant patches of orange, red and gold. The females tend to be a more demure brown or blond. I say most of them, because I have gotten a few males that are on the lighter side, and a few females that are on the redder side. But, it does work for most of them, still have to wait and grow them out for a bit first though.
The Roos certainly do have the redder plumage , but that is generally only obvious once the hormones kick in. By that time there are other indicators quite obvious in regard to sex. So I'll stick with my response, ' not a reliable sexing method ' .