I personally use Paint.net, specifically playing around with the Recolor tool but the recolors I do take quite a bit of manual coloring as well because the recolor tool can be pretty hit or miss depending on how high you can get the tolerance, how high rez the photo is, how clear the colors are etc.
I'm surprised that nobody had the idea to paint their O-12 with the Star Command color scheme. Not that it's super colorfull but I find it pretty fitting to what O-12 is in the Human Sphere.
I'm going to go full Carolean as an adaptation of the official scheme. Deep blue on the outside, yellow on the inside of clothes/cloaks, beige-yellow leggings, black shoes and gold armour details. Contemplating whether Hippolyta gets to wear the above Bureau Aegis colours or if she gets colours from one of the more local regiments like Närke or Savolax (blue outside, red inside) to mark her "auxiliary" nature... and as I'm typing this I'm struck by the thought of painting Gamma and future Zeta in artillery colours (grey outside and blue inside and blue details).
A quick test gave me this. Alternatively I was thinking dark blue hard armor parts, dark grey clothing and try out fluorescent yellow on the mesh parts.
What i plan to do is to reach out to Mass Effect for inspiration and do them like Cerberus. Then again white/black is pretty boring so i will add that yellow they used for markings as the shiny areas on the dossier and do a lot more markings than in the game. Epsilon and Delta will be black/yellow as were the special operatives in ME3
That's how I was doing my CSUs and ALEPH units for my NCA. The black and white with splash yellow works well.
Paladin is the way i intended to paint mine : white and gold scheme, with cold shadows on the white (using dark blue gray like the fang)
My fellow O-12 commanders stationed on Novyy Bangkok will have already seen these, but here's how I've colored my detachment.
If you're looking for it to do some hard highlights on the shoulder pads/armor plates, look at Gryph-Charger Grey(Contrast) instead. When used alongside of the medium, the contrast stuff is amazing for doing that kind of line-work. Never thought of doing it myself until I sat through the step by step of the Wild Hunt from the Beastgrave setup, where they use Black Templar heavily thinned down with Contrast Medium to get some really nice blacklining going.
Try Warp Lightning and Aethermatic Blue from the Contrast range. It's great for that kind of stuff, assuming you base the area with white first.
Now that I look at the O-12 figs, they’re very nice looking (and crack a Smile on ”Kyttä Copperbot” name’s Finnic-Ugrian slang word meaning ”cop”) xD