Cerakote makes a C-Series Cerakote that is air cure. Thats what is used on optics.
I have found Brownells Aluma-Hyde II to work very well once fully cured. If you can leave it alone for 7-10 days the Aluma-Hyde II sets up very durable.
Alumahyde II Coyote is a near perfect match for Magpul's FDE and the Cerakota is godo to. I have a 3 gun rifle that is done in that color. In this photo the Rail/Lower/Upper are done with AlumahydeII, the AFG/Sights/Stock& Grip are stock Magpul FDE and the Silencer is Cerakote FDE. The Alumhyde II appears a little darker in the pic than it does in reality.
I've used DuraCoat a few times. Manufacturer of DuraCoat Firearm Finishes: Shake 'N Spray
For about $40 shipped you can get a shake 'n spray kit in one of a gazillion colors.
Two part epoxy coating applied with a disposable air brush like applicator.
I do 5 to 6 AR lowers or uppers with one kit (3 coats each).
A few weeks at room temperature to fully cure and it's pretty tough stuff.