A few months back I stated on this list that "camo gear isn't very useful'. I am now revising that statement to:
"Camo gear is not significant ... unless you intend to do something like a blind or sitting in one spot for a long time in order to get a look/photo of a bird that is often unapproachable." And especially if you are going to "wait for the bird to come closer to you".
What camo does is to minimize the perception of movement or presence by birds - it does work. It's really a matter of "how much" more than "if".
However, I still say that in my experience it is "movement' and especially "movement in a direction that brings you closer to the bird" that is most important. And more important than the clothing you wear or how much noise you make - of course, darker/less contrasty clothes and quiet will decrease a bird's flushing due to your presence. And, again, each species seems to have it's own "how close/how much movement" limits ... and individual birds of a species can be more/less sensitive that the general limits of its species. Sometimes significantly. And that, in general, if you have a camera and a specific lens (my primary focus) then the size of the image in the view screen is "pretty much the same for all birds of all species" in terms of how close you can be before they flush. Get a picture, move a little closer, get another picture ... and watch to see when the bird(s) get "antsey" ... that's going to be about as close as you will get before they more away. Some species will fly, some will only walk/waddle/swim further away (ducks, geese, swans in particular).