Our yellow squash has some brownish discoloration inside in a ring down that extends length-wise. Is this normal variation and safe to eat, or is this an indicator that the squash has gone bad?
This can be one of two things: 1) If you bought this from a store the squash is a bit old. It own't hurt you as mentioned in one of the comments above it just isn't pretty. 2) If this is a fresh squash, if you had a heavy rain storm or a higher than normal concentration of smoke in the area (like forest fires) then it is possible for excess minerals to be deposited in the meat of some veggies (squash is among that list).
Either way it won't hurt you.