[yoni0505]

to check if someone is team attacker(killer) check onplayerdeath if the killer's and the victim's teams are the same, if they are, set a variable such as teamkiller[killerid] to 1.
after that, make a checkpoint and when a player enter make an if(); that check if the player is a killer (if teamkiller[playerid] equal to 1), and if so, start a 10 seconds counter that will call a public function that set yellow[playerid] to 1.

thats pretty much the idea