When you think about it there are a lot of Superheroes and only a very few truly iconic costumes. Almost everything else takes off from those. Here are a few jumbled thoughts about them.
Spiderman has probably one of, if not THE very best costume for concealing his identity. The costume covers his entire body, showing not one bit of flesh, and lenses cover his eyes. There is nothing about Spiderman’s costume that can give away his identity. No skin, hair, or even eyes show through. You don’t know if he’s a black guy, a white guy, asian, Martian, or anything else. The only thing the costume gives away is his build, which is lean and athletic like an acrobat. And meanwhile Peter Parker tends to wear clothes that don’t really show off his physique. He plays the wimpy guy, not wearing tight clothes or sleeveless shirts. So even someone who knew him particularly well wouldn’t even make the distinction that he has the same build as Spiderman.
Strangely at the same time his blue and red costume doesn’t really evoke the image of a spider. Blue and red are powerful heroic colors, so in spite of the spiderweb overlay and the big spider symbol dead center, he doesn’t evoke the image of a big creepy predatory arachnid, which lends more to his playful bantering character, who takes advantage of villains underestimating him. This provides complete contrast to another hero based on a traditionally creepy animal.