My Observations:

First the obvious, the more clear the water, the more this issue comes into play. I've caught fish less than a rod length away when there is <2' vis. In normal to poor vis, I don't think its an issue, as long as you don't do anything too extreme (like fall in and go swimming).

In clear water, I've found that new arrivals can be veerrry spooky. Early summer after snow melt and rivers start to clear, I've seen fish turn and burn out of hole when a smolt flashes near them.

Fish get used to the commotion. At terminals like Reiter in September, the fish tolerate people movement and line after line after line going through them. They are not aggressive biters, but keep it small and keep changing up, and eventually you'll peak their curiosity.

I'm a strong advocate of not wading when you don't have too (real strong). The fish can sense movement in the water with their lateral lines, and even during perfect vis conditions, excessive wading will turn aggressive fish into September Reiter fish. I think acclimitized fish will tolerate people standing high profile on the bank (like on a boulder holding your float rod above your head) more than standing too close to them in the water. I know folks that only spot fish during the summer, and do it successfully. And if you can see them, you know they can see you.

Surface ripple may be just as important as clarity in clear water. The more the surface currents break-up visibility to the bottom, the less spooky the fish.

If fish can distinguish different color corkies, they certainly can see colors above water. It just makes sense to wear subdued cloths in clear conditions. I don't think it necessary to cover up, although you'll usually see me at the terminals come August and September fishing those non-aggressive but acclimitized fish. The surface ripple issue probably minimizes the importance of looking like a live predator.

I do think keeping still is important. I just go through the normal movements of casting and drifting.

In my opinion, talking is not an issue. There is a lot of ambient underwater noise associated with a flowing river. Maybe in lakes...

Can't tell you how many fish I've caught 10 minutes after a sled zooms through, a drift boat passes over, a white water raft moves through (neon yellow in the dead of summer). I'm a believer that moving the fish around will make them more aggressive and will occasionally rock a hole.

All I can think of..