aircraft disappearing against terrain.

[Romanator21]

I'm just going to echo what's already been said, and mention that it is indeed hard to spot planes in real life - and all the planes I've seen were glossy white, not camouflaged.

Scan just a certain "sector" of your field of vision at a time, using your peripheral view to detect moving objects, or even stationary faint ones (For instance, I tend to see stars better when not looking directly at them).