Stress and poor lighting can cause most any frag to "brown out". I wouldnt neccasarily avoid a brown frag... there are a lot of people out there that have purchased a brown frag and have it turn into something incredible!
i like brown frags they are like little suprises (whats it going to look like) and they are usually cheaper. just make sure you have good water quality and it should be fine.
Alot of chalices will brown-out temporarily after being cut. My Ktar's Melting Pot was cut back in the middle of April and is just now starting to get some deeper coloration.
I got a huge oregon tort for a very good price and it was brown, so brown I thought it was miss ID'd by the guy I bought it from even though he clearly knows his stuff... It has since started to color up really nicely and I think I just got a frag from the underside of his colony that was growing up against the glass (flat spot on the frag) so it wasn't getting great light...
every chalice i have ever purchase was brown when i got it. when i frag they will sometimes brown out for a bit as well. next time your at your LFS and see some brown ugly chalice for sheap buy it and bring it home. you will almost always be very glad you did
About comments are true. But you need to know that some corals turn into brown easily and some do not. If you are suppose to get a frag of OME, and it looks brown when you get it, then there is a high chance that you got a something something else.