Open zombie_plague_advance.cfg (zpa) and Find this // Flashlight & Nightvision Here edit this :
For zombies :
zp_nvg_color_R
0 // Zombie custom nightvision color (red)
zp_nvg_color_G
255 // Zombie custom nightvision color (green)
zp_nvg_color_B
255 // Zombie custom nightvision color (blue)
For Humans :
zp_nvg_hum_color_R
10 // Human/Spectator custom nightvision color (red)
zp_nvg_hum_color_G
10 // Human/Spectator custom nightvision color (green)
zp_nvg_hum_color_B
10 // Human/Spectator custom nightvision color (blue)
Go here
http://www.rapidtables.com/web/color/RGB_Color.htm and select the color you like.
After take the numbers from R G B and put them instead of where i put the red numbers here, those number of the color choosed from rgb site.