When out birding I almost always wear a thin khaki green fleece (well, summer has not yet fully arrived here), complemented with no logo whatsoever. This appears to have been the manufacturers choice. The fleece cost £4.99p from Tesco, and a logo would probably have doubled the cost! I personally find it warm enough for me, plus it is virtually soundless. Waterproof it may not be, but then again my health dictates that I am a fair weather birder.
As for headgear, then it just has to be a plain, no logo, green baseball hat (I am bald and would stand out quite significantly. This also acts a a sun visor, and I think helps cover part of the face up from the angle of a bird looking down, eg the extended peak.
Sir's outfit this season is completed with a pair of jeans and matching pair of trainers.
The whole idea of getting close to nature is not to wear bright, gaudy coloured clothing, rushing around, making as much noise as you can. I usually walk around 12-15 steps; take care where I put my feet (twigs, leaves etc); stand; and just look and listen; often leaning against a tree for 4-5 minutes before moving on.
This "system" seems to work well enough for me.
Regards,