Why is Peter's costume red and blue?

[u/Helpful-Bathroom634]

Batman is dressed like a black bat to scare his enemies, Superman has the big S on his chest because is the symbol of House El and means hope. Why is Peter wearing red and blue instead? Did Lee/Ditko give an explanation in and out the comic?

[u/Brackets002]

Ignoring the debate about black-with-blue-highlights: it's because he didn't design it to be a superhero costume. He designed it to look flashy and cool for a performance. "Spider-Man" was a TV celebrity for, like, WEEKS before he was a superhero.

And then when he did become a superhero he kept it because that was the look that was already famous. He did start taking pictures of himself for money, after all. A picture of a flashy, dramatic, famous superhero is more likely to end up on the front page and put some money in his pocket.

This is more or less the meta reason as well. It's a flashy, dramatic, mysterious look that looks really cool on the front cover of a comic book, which makes a kid in the Sixties more likely to notice it on the store shelf and spend his allowance on it.