This simple addon adds pink crosshairs to match Half-Life: Prison's pinkish HUD.
To install these crosshairs, extract the ZIP to somewhere like:
C:\Program Files (x86)\Steam\steamapps\common\Half-Life\prison
Exit and re-enter Steam, run the mod and the crosshairs should be Pinkish color.
I'd like to thank someone who helped me with several of my Half-Life: Prison add-ons and that is Lime at Moddb.com - as they've helped me to decide several things around this and I was generally just asking them things while I was doing them.