I'm not in the USAF, but from what I understand, it's not exactly the most popular uniform with airmen. The tiger-stripe pattern has been criticized for being ineffective in tactical environments - complaints similar to those about the US Army's Universal Camouflage Pattern (UCP). The Warhammer 40,000 universe, however, has many more types of environment than Terra does. The ABU tiger-stripe camouflage still looks cool. So somewhere in the vast but grim darkness of the far future, surely there is a place for the ABU.
The Airman Battle Uniform consists of all three of the same colors of the US Army UCP, that is, Urban Grey, Desert Sand, and Foliage Green. However, the ABU contains a fourth color, a slate blue that shades the pattern ever so slightly. In the images here it's hard to pick out.
So onto the tutorial. I painted the lasgun Chaos Black/Abaddon Black, the clothing Kommando Khaki/Karak Stone, and the boots, belt, chinstrap, and parts of the helmet in Vallejo's 830 German Field Grey. In the past I've used Codex Grey/Dawnstone to represent Foliage Green, but I have since found that 830 German Field Grey is a much better match.
Next I began painting on the tiger stripe pattern, with wavy lines in Vallejo's 886 Green Grey. The lines should be painted generally horizontally.
And then comes the next step, which is key to making the ABU tigerstripe pattern look right. The next color, 830 German Field Grey is not just an overlaid stripe pattern, but rather, it fits within the existing Desert Sand color. If you look closely at the image below, you'll see that there are few places in the pattern where the two greys touch. Almost everywhere they are separated by a thin line of the Desert Sand color.
In order to achieve this effect, you have to paint the 830 German Field Grey in the spaces between the 886 Green Grey, but make an effort to leave the tiniest amount of Kommando Khaki/Karak Stone/Desert Sand between them. It's ok if they overlap in a few places, but it should be rare.
The final color in the pattern is the slate blue. I have not found a perfect match yet for this color, but I managed an approximation with Vallejo's 816 Luftwaffe Uniform WWII with a very small amount of Chaos Black/Abbadon Black to dull it down. This color is present in the ABU pattern in very small amounts, so I delicately placed little dots and tiny stripes in likely places in the pattern, keeping it subtle.
Finally I put on the static grass on the base and highlighted the lasgun, boots, and a few other details. I did not quite enhance this last photo as much as I did with the others, as I believe this image below better represents what the model actually looks like. I think the colors match pretty well to the ABU's appearance.