Batman was actually blue in the 70s, and in the Hush story.
Well, see, when these characters were first created, they were wearing black suits. At least, Spider-Man was (I’m only applying the same logic to Venom). My assumption is that the lighting of 2099 is so strong (everything is bright and neon) that they were mostly highlighted, and the highlight color of choice for black back then was blue.
The funny thing is that Spider-Man was only mentioned as being in a black suit through dialogue, and since many people haven’t actually read the books, they just assumed he was blue. Many appearances later and he basically was blue.
So they started out as black, but the blue stuck because it was so prominent.
Don’t sweat it, the whole thing is weird and confusing.
Probably would just have to go SUPER sharp and spiky I suppose. Over-the-top almost.
But either way, it still looks awesome!