Hi All: I do observation of a bald eagles nest at 33M range (by triangulation), on a cliff slightly above the nest, so I am able to use the cliff as a hide, next to the bole of a spruce tree.
I just use low profile clothing, gray, green, brown, and cover up the hi-vis parts of my bike gear.
Because of the cliff only my head and top of bino+tripod are visible from the nest, so I use bike inner tube rubber bands on the tripod (black matt spray-painted) + binos to attach dead evergreen branches.
I pull a camouflaged (US Marpat) stuff sac on top of my balaclava, so it breaks up the outline of my head.
I have switched to dull plastic water bottles, and keep bright stuff inside another big (US ACU pattern) stuff sack.
My foam sitz pad is grey.
I am 75% covered by overhanging evergreen boughs, but I did buy some MARPAT pattern nylon scrim mesh net, which is clothes-pegged (olive spray paint on the pegs!) to the branches.
I use the scrim net as I do not want to spook the parent Eagles as they roost around the nest, or swoop in to feed the eaglets, it sort of fills in the gaps between the boughs.
Much of this takes place at -10C to +15C, so cold enough that I use a Norwegian Fjellduken sleeping-bag-poncho-tarp in a lichen-covered-rock pattern to stay warm over the hours.
Other locals don't bother with all this, but the locals also drove the last pair of eagles off of a more-publicly accessible nest site....
I don't want to be blamed for that!
Oddly enough, the eagles don't seem to feed their young when obvious people are around the nest....
I bike into the site, then hide the bicycle under a tree, with all its hi-vis bits tucked away.
I approach the hide site using the lip of the cliff as cover, then scoot under the branches of the tree to set up the hide.
So, if you use the terrain well, exploit cliffs or folds in the land, are able to stay in place for multiple hours, then dull clothing and equipment will probably do. Scrim net is now in nylon, dries quickly, packs very small, and is low cost. But you have to use natural cover first...
If you wander around full upright, in plain sight of what you are observing, even a Ghillie suit won't be much help!