I don't remember how to do these; there should be videos and maybe even a how-to on a Camry forum. There's a video from Weber University that may shed light.
If I had 100k I would do a pain drain, then refill, then pull the cooling line and do a full exchange until the ATF ran clear. Bit of a pain to get level correct; car needs to be reasonably level but you have to be underneath at the same time, so it's gotta be up in the air, then at the right temperature to pull the plug.
Depending on your background it may well be easier to let the dealer do this, if the price isn't bad. No idea but it's probably what $200-300? Seems like "too much" for a few quarts of oil but I am pretty sure I killed an afternoon doing it on my much easier to access truck, where I didn't need to raise it up, and I didn't bother with changing the filter (I did a few years ago and IIRC it's not really a filter but more of a strainer; it's only ever gotten light usage since).
I would not sweat the fluid color too much: almost every thread about Toyota WS fluid has complaints about it looking awful. It seems to change color fast. It may well be due, I'm not saying otherwise, just that you shouldn't assume the worst just because the fluid looks dark.