Fabric paint on webbing

I've noticed that if I pick up one of my love-tissues, that are approx 6 days old, they've turned a sandy brown colour. Perhaps you could try wanking over your webbing?
Rope your webbing onto the back of a wagon and go off-roading with it bouncing around merrily behind you. Will age your webbing in no time.

When did you last see a painted bush outside of Disneyland?

Why not give it to that soapdodger off strangeways last night. A week with him it'll look nice and tanned. Scruffy Cnut. Anyone see his nails? Nice
If you give it to a real soldier he will take it away for six months and get it looking used for you. Might even get a 7.62mm hole or two in it to add to the authentic 'used' look.
krylon is the daddy for spray painting equipment. But for you to age/dull your webbing I would find/make a big muddy puddle and chuck it in there get it covered dry it out and try brush it out with a dry scrubbing brush.
I just used regular fabric paint to turn my Coyote Tan daysack in to something like DPM. It give it that well worn look, mind you I have been using it for 6 years so that might have helped.