Turn items inside out before washing.
I also use Woolite Extra Dark Care; you can also use any baby-safe laundry detergent.
Use cold water.
The only time you should use hot water is if you need to clean off poison ivy/poison oak. (and in those cases you'll likely agree fuck the colors, you don't want reoccuring poison ivy outbreaks everytime you wear your BDUs). Poison ivy is an oil (Urushiol) and should be cleaned as such if your clothes come in contact with it.
Never use fabric softeners on wicking or breathable fabrics (the fabric softeners will interfere with it, they can clog the micro-pores that make a fabric breathable); for the same reason, don't use excessive amounts of laundry detergent.
Also, less critical for airsoft, but maybe worth mentioning if you're using your gear for outdoor activities like camping (camp fires), or if you play with pyros: fabric softeners are flammable. That's why Nomex garments are always labelled No Fabric Softener.
Leaving BDUs (or any clothes) dirty is counter-indicated [other than for the obvious reasons] since dirt will weaken fabric: so your BDUs might not fade but they'll wear and rip prematurely.