Long ago I read a report by some sniper instructors who used neon flagging tape as a marker on long known-distance ranges. They used their cadre and students as evaluators to see which color was most highly visible. The consensus was that neon pink stood out the most. I don't recall which environment the range was in.

I think just about anything bright will work for your gear, though snow could be a complication. Peter Kummerfeldt says that red paracord works well against snow.