Why Is the Rifle Icon Red?
If a weapon icon is RED that means your character is unable to use it due to one of their Injuries.
Check their character icon and there may be a head icon with bandage wrapped around, this means they are injured.
If you look at your character sheet and hover over the injury it will say what the injury does.
Some of them are minor like slows down movement speed or lowers hit chance, but some are major where you can’t sprint or use any rifles/smg/shotguns, etc.