Puddles like these are caused by oil floating onto the top of a puddle, reflecting light in the same way a rainbow does, causing a variety of colours.
Oil usually builds up over time on the roads, and without any rain to wash it away it just sits there, until rain finally comes mixing water with the oil.
love fics where Danny ends up in the DC universe & every alarm goes off at once & the magic users are like "yeah that's the most powerful being in the universe & also possibly super evil we are FUCKED fucked" & the Justice League is freaking tf out trying to find this thing that casually tore a hole in reality & it just cuts to Danny (Fenton) standing in the background blissfully unaware & like "man my life sucks but at least i have this candy bar—" *drops it in a puddle*
I love the tiny little lines in ghosts that really show just how thoroughly of their time period they are. like kitty's "pineapple, goodness no! they were wealthy but they weren't royalty!" and everyone being enamored by the shiny circle and julian going "it's a compact disc" completely unimpressed, and pat's "that is the front bit of a television. don't know where the back bit is, but that's the front!" like. something about the casualness of lines like that where they're just so completely them, fully realized characters from the get go. it's so good.