cl_crosshairalpha <number>
Sets the crosshair transparency from 0 (invisible) to 255 (fully opaque). Only applied when cl_crosshairusealpha is true.
Examples
cl_crosshairalpha 200 - Default transparency.
cl_crosshairalpha 255 - Fully opaque crosshair.
cl_crosshairalpha 100 - Half-transparent crosshair.