I've only found this possible with one camouflage option: Moss, obtainable from holding up The End three times during his fight.
Once you obtain Moss, equip it and go to Sokrevenno North (one of the three areas that the fight takes place). There are some "bright" dark green patches of earth within this location. Crouch and crawl over it and you should see your Camo Index reach 100%. If not, you can also equip a face paint that'll help (though it might only give +5% maximum through that). This will also unlock another trophy if you've yet to get it: