At first I thought "wow, at last, a simple and easy-to-do change that might improve the game". Then I checked a video and, er...
Am I wrong, or are the two players using pink and blue reticles, as well as having the 1UP and 2UP icons in different positions?
You're right, but the pink recticle displais only when you got a new gun. Other minor difference is that the player 2 cursor flickers all the time. The solution could be to change that insane flicker effect for a permanent color instead, green for example.