Hay tends to turn brown as it gets older/stale, too, so in stores at least, I try to get the (naturally) greener stuff. A lot of commercial hay sellers actually dust/dye the stuff they bag for small pets. Oxbow doesn't, but I know Kaytee and LM Animal Farms are WAY too bright green, even compared to fresh hay, to be completely natural. That said, I live in "Little Peru" in western NY-- there are over 40 alpaca farms within an hour's drive of my apartment. The hay I get from one of these farmers is a pale peridot/lima bean color with some brown stuff, smells AMAZINGLY sweet and fragrant, and the chins go bonkers for it. Next to the bag of LM Animal farms stuff I had to get last week, it looks somewhat 'brown', more like the stuff you kick off of your shoes when someone mowed a lawn and left the cuttings to lay (which is essentially how hay is harvested). I'd say if there isn't *any* brown in a bag, don't buy it (evidence that it's dyed), but there should be more green than anything else.