just open the sight in PAINT and FILL the black lines with the color you want.
Edit: Hmm.. I tried doing that.. but it doesnt change to red color. Weird. Sorry, I really dont have a clue. I tried changing the gunsight color to grey, to red , to pink, to cyan.. when I put it on AH offline they either looked black or white or dissapeared (pink).
I just uploaded an updated sight in my first post, I noticed the tick markers for the 20mm's and rockets were too high up.