blacktail

This is my first time with sex links - I bought six Columbian blacktail (white Sussex x Rhode Island Red) eggs from a farm that I have used many times. I ended up having two pulleys out of that that I sexed at hatch. However they are now about 15 weeks old, and one is presenting in my mind how a...

Could anyone help me out with sexing these chicks? Lighter one I think is a blacktail and darker one is RIR. I won't put what I think their genders are so I don't influence anyone😬! Any suggestions appreciated!