As with the woodland MARPAT and the desert MARPAT, I made a swatch and compared it to a sample of the real thing in an attempt to match the colors. In this case, the colors match pretty well. The colors are Codex Grey, Fortress Grey, and Dheneb Stone.
Before I jump right into the model itself, I thought I'd go over trying to figure out how to paint a digital pattern. The simple fact is, at the scale of these models, there's no way you'll be able to match the real pattern--the pattern itself is too small and complex. The best you can do is approximate it, with the knowledge that your brush is just too big and clumsy to get the real thing down pat.
I played around with Photoshop to analyze the pattern. On the left is a photo of an ACU, and to the right is the same photo, but blurred. The blurring simplifies the image into more managable shapes.
Next I used the brush tool to paint over the dark grey areas. Due to the sheer coarseness of the brush, you lose a lot of detail, but I'm only worried about getting the basic regions of color here.
Next I used the lighter shade of grey, and painted over the areas where that color seemed to be most prominent.
Looking closely at the picture, it's clear that I missed a few spots, so I went back and touched it up a little, filling in some more areas with the two greys.
Finally, I replaced the background of the painted image with the sand color. This solidifies the image and you can see its constituent shapes.
The end result is clear: The pattern does not consist of stripes of different colors, but it's not just irregular blobs either. There are sections of the dark grey and the sand that have the appearance of stripes, but they are definitely irregular in thickness, and they are broken up by the light gray, which is very randomly distributed.
So how does one paint this? I would suggest starting off by painting irregular stripes, and specifically avoiding keeping them of uniform thickness. In fact you should actively attempt to keep the thickness random. Then paint on random dabs of the light grey color. Once this is done, hold the model at a distance and examine it--if it looks like there's too much sand, or too much dark grey, you can touch it up by randomly applying dabs of the deficient color. Do that enough times and the digital pattern will start to emerge.
Stage 1: Ok, so here I go painting my actual model. Step one was to basecoat the model. I gave the skin a coat of Tallarn Flesh, the cloth Dheneb Stone, the armor and boots Khemri Brown, the gun Chaos Black, and the gloves and accoutrements Orkhide Shade. I know what you're thinking, "Why Dheneb Stone for the basecoat?" The ACUs are mainly grey, not beige... Well, in the real ACU the sand color really does make up a significant amount of the pattern. Practically speaking, the Dheneb Stone is a foundation paint, and therefore covers the black basecoast very well--better even than Codex Grey. If I did Codex Grey, I'd probably have to do two coats to cover it the black uniformly.
Stage 2: I painted the armor and boots etc., with Desert Yellow. I agonized about what color to use for a long time. When the ACU was first fielded in the real world, the body armor of troops varied widely in colors because of what was available at the time. This included old woodland pattern, olive drab, coyote tan, to foliage green (the darker grey in the ACU pattern itself). Nowadays, body armor in the ACU pattern itself seems to be the most common. This might look cool, but the entire model would end up looking like the pattern, blending in with himself and obscuring the detail, which would detract from the appearance of the model. This picture is an example:
Seeing as I'm painting up many of my troops in the woodland MARPAT camouflage, and they are issued Coyote Tan body armor, I decided that this guy would have been issued the same thing. At this stage I also picked out a few spots in Chaos Black, and painted the scope and laser designator with Regal Blue and Mechrite Red respectively. I also did a very heavy drybrush of Catachan Green over the Orkhide Shade areas.
Stage 3: Next up was starting on the camouflage pattern itself. I painted Codex Grey over the cloth in an irregular stripe pattern, dabbing it on in places to make the stripes irregular in shape and thickness. I deliberately gave the Codex Grey a lot of coverage, so as to tone down the dominance of the Dheneb Stone.
Stage 4: This next stage was very simple--I painted in the eyes, then gave the face and all the Desert Tan areas a wash of Devlan Mud to shade them. The wash on the armor also darkens the shade a bit to make it match the color of Coyote Tan a bit better. I also gave the face another wash, this time of Ogryn Flesh.
Stage 5: Now I dabbed in Fortress Grey into the camouflage pattern, randomly and comparatively sparingly. Anyplace on the model that looked like the Codex Grey was over-dominating the Dheneb Stone or vice versa got a dab of Fortress Grey. Once that was done, I did a once over and touched up any places I thought I missed with Codex Grey and Fortress Grey. At this stage I higlighted the face with Tallarn Flesh, the armor and boots with Desert Tan, and the green areas with a 50/50 mix of Catachan Green and Knarloc Green.
Stage 6:Seeing as this guy is a sniper, I did some web-surfing to look at some sniper rifles to look for other paintjobs than simple black, and found some cool pictures of the M110.While I didn't model my sniper rifle on this design, I decided to paint it similarly. I painted the casing with Khemri Brown and highlighted it with a 50/50 mix of Khemri Brown and Kommando Khaki. I painted the imperial insignia on the gun with Desert Yellow and gave it a wash of Devlan Mud. I painted the scope Charadon Granite, and hightlighted various black bits on the gun with Charadon Granite as well. At this stage I also finished up painting the scope and laser designator, and highlighted the various black bits of the model with Adeptus Battlegrey.
Finally, for fun I also decided to give this guy some Nomex Aviator Gloves, just like the guy in this picture.Nomex Aviator Gloves are in pretty common use, based on various photos I've seen of troops in the field. They are basically green on the back of fingers/hand, with grey on the palm, inside of the fingers, and a stripe that runs between the fingers and thumb down to the wrist.
With that, this guy is good to go...