For what it's worth.... I own a 92 Camry 4cyl. A transmission shop owner told me yesterday to make sure that when you take your Camry in for service, the oil level be checked in the tranny. He is not talking about the dipstick, but a gear box of sorts that is part of the tranny. It contains 90 weight oil. It doesn't have to be changed but should always make sure it's full. You have to remove the fill plug to check it. If it gets low, it burns out the seal which lets the 90 wt oil and the tranny oil mix. He showed me the $1500 results of one that was in the shop. Not pretty. He said most shops never check this on routine service.
I would also guess that if your tranny dipstick oil is dark, one possibility is the gear box seal has broken.