Yeah you can do this:
bind "1" "slot1; exec defaultcrosshair.cfg; cl_crosshair_red 255; cl_crosshair_green 255; cl_crosshair_blue 255"
bind "2" "slot2; exec defaultcrosshair.cfg; cl_crosshair_red 255; cl_crosshair_green 0; cl_crosshair_blue 255"
bind "3" "slot3; exec defaultcrosshair.cfg; cl_crosshair_red 255; cl_crosshair_green 255; cl_crosshair_blue 0"
In this, defaultcrosshair.cfg would contain cl_crosshair_file ""