There’s two issues here, paratroopers and folks bailing out. Paratroopers are active soldiers who are entering combat, and it’s expected that they’ll be shot at, and shoot back. As such, it’s to their advantage to use inconspicuously-colored parachutes: Green might have been chosen rather than blue to make them less noticeable once they land.
On the other hand, a person bailing out of a crashing aircraft is a casualty, not a combatant, and is therefore protected by the rules of warfare. Provided that everyone’s playing nice, they aren’t at any risk from getting shot, but they are potentially at risk from starvation, exposure, wild animals and such until they get rescued or otherwise get to safety, so it’s to their advantage to have bright-colored parachutes.
The rules of war aren’t just something that matters if you lose: Violating them is likely to get a lot of folks mad at you, and may well turn a lot of nations from “neutral” to “enemy”.