i dont know about khaki, but white and grey can get dirty pretty fast. especially around the cuffs of the sleeves. also, if you bail on rails you can get REALLY dirty.
I rocked all white last year and it definitely got torn up. Got some paint marks from rails, grease from riding the T-bar ont he back of the jacket, etc. And no, there is no great way to clean it. That is just what you accept if you rock white stuff
I had kahki pants for the last two seasons. They didnt get dirty except a few marks from rails like said above.. You usually can get them out but I have a few that didnt.