//First you must create a autoexec.cfg, then you must typ this:
alias ch_sw "incrementvar cl_crosshaircolor 1 5 1"

//In the next step you must open your config.cfg and add this text:

bind "W" "+forward; ch_sw "
bind "s" "+back; ch_sw "
bind "a" "+moveleft; ch_sw "
bind "d" "+moveright; ch_sw "
bind "MOUSE1" "+attack; ch_sw "

//Now your crosshair will change the color, everytime you press one of //this key's

//Hope it will help you and happy fragging :o)