Red and silver combos show up everywhere if you start looking, but the pairing is almost never about the colors themselves—it’s about the clash of ideas they represent. Like 'red' could be Gryffindor bravery, while 'silver' might be Slytherin cunning. That’ s why Harry Potter fanfiction latched onto Harry/Draco so hard; it's the poster child for this dynamic. But you can find the same push-pull in Marvel with Iron Man (red armor, flashy ego) and Winter Soldier (silver arm, haunted past), or even in 'Naruto' with Naruto's fiery orange-red energy versus Sasuke's cool, metallic Sharingan silver. It's a visual shorthand for 'opposites attract' or 'enemies to lovers,' which is basically catnip for fanfic writers.
I've read stories where the colors get literal, too—like a 'Final Fantasy VII' AU where Cloud's red motorcycle jacket contrasts with Sephiroth's silver hair, and the whole plot revolves around that stark visual difference. Sometimes it's just aesthetic, but often the theme digs into redemption arcs, hidden vulnerabilities under a cold exterior, or a hot-headed character learning restraint from their calmer counterpart. The most memorable ones use the color motif to reinforce emotional beats, like a silver character finally showing a flash of red-hot anger.