This is something I've been noticing lately. Background: I've been paleo in diet for about 9 months, only in the last 1-2 months have I also primal-ized my lifestyle and begun to exercise more regularly (following general advice from Mark Sisson).
I hydrate well, always have, but I've been noticing in the last few weeks that no matter how much water I drink that day or right after exercise, my pee is a really dark yellow. There's nothing wrong aside from that, except maybe I have more energy than usual :-), but I just find it so odd and maybe slightly alarming.
For reference, the kinds of workouts I do vary, but are sometimes yoga, bikram yoga, 20-30 min sprint intervals running or on the elliptical, and body weight exercises. When I work out, whatever I'm doing, the total time is 60 to 90 minutes of pretty intense work with minimal rest. I don't hydrate while exercising because it gives me cramps.
Any ideas on what's going on here? I had bloodwork done a few months ago to test for Crohn's and all the kidney stuff was normal, so I don't really think it's something to be scared of, but what could it be?