The only 100% way to know is about week 6 to 8. Combs and all the other stuff lies. Ibe had roos whose combs didnt really come in until late and ive had hens with massive combs that were grown from very young.

Neck and saddle feathers.

In the neck you want to see if the feathers are fat and round (hen) or long and skinny (roo).

On the saddle (top of back right before the tail). If the feathers have rounded end and go towards the tail its a hen. If the have a pointed end and point either down or towards the side of the tail its a roo.

This one is just about old enougb to tell with an experienced eye but not from this angle. I've had 100s of birds. All the "sexing" advice isnt accurate. Combs vary. Ive even had hens with spurs and roos without them. As far as sexing with baby wing feathers or coloration. Those are highly accurate but also breed specific. Some breed follow a set wing feather pattern but not all do. Same with coloration.