Box dyes are definitely not reccommended for this! What I use is body hair bleach, as I read in a couple of magazines.  It's about 5 bucks for a tub, and the tub will last you FOREVER. Just mix the creme and the powder together and spread it over your eyebrows. It won't take a very long time, so check it every minute...you won't be going overboard to check every 20 seconds, this stuff works fast; especially if you want a very subtle change. The regrowth is practically unnoticable (by that I mean only noticible to you). I've done this tons of times, it looks super natural- just make sure you check your brows obsessively while they are processing.