The original topic was picking fields.
whereas 'brown' fields are probably earth or stubble, so a better bet.
As an ex-mil helicopter pilot, I've had a lot of experience of routine landings in fields. It's really not a good idea to ever pick a brown field. A brown field will have been ploughed and will be much softer than others around it so the likelihood of an aircraft nose-over is increased, especially if you land across the furrows.
I used to instruct on the Bulldog. In that aircraft (and many other low-wingers with a sliding canopy), if the aircraft ends up on its back you will possibly be unable to escape without outside assistance, which may not be forthcoming in time if the aircraft goes on fire. The RAF latterly equipped the Bulldog with a pathetic little belt cutter/escape hammer, but I'm not certain that the hammer would be effective in breaking the canopy. Even then, if you broke the canopy, the aircraft would possibly fall on you!
I wouldn't let any of my students even practice PFLs to ploughed fields, in case the engine didn't pick up for the go-around and we ended up in there for real.
My best friend, another RAF QFI, died in a Bulldog forced landing, btw. The aircraft stayed upright but a very poor choice of field resulted in a very severe impact which he didn't survive.