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Coturnix quail that are solid brown like your picture can't be sexed by feather color or markings. The boys look exactly the same as the girls. You will have to wait until it is a little more mature, closer to 6-8 weeks to be able to either vent sex or have it display male or female behavior. To vent sex you hold the bird gently upside down so you can see the vent, then feel for a small bump next to the vent towards the tail side. If you can feel a bump there and gently press on it and white foam comes out the vent it's a boy. If there is no bump or foam, it is a girl.
I've had boys start crowing as early as 5 weeks, and girls start laying as early as 7 weeks, but individual birds vary. I had one hatch where I separated the boys out as soon as I could tell their gender, and there were some that were way on the early side, and a few others took till week 9 to start acting like boys and crowing.