i've noticed in team servers that there are some people who shoot their team mates. some do that on purpose but i do know that there are some people who are color blind.
if you are color blind this should help show who is a team mate or enemy.
open the game to the main menu....then go to setup. click on game options.....go to crosshair settings. here you can change the crosshair size, shape, color. you would rather have the crosshair color to be white same as the scope color.
but change the crosshair color friendly to black....do the same for crosshair color friendly scope.
this is my settings for the crosshair colors:
this should help those who are color blind.