Here's a step by step guide on how I painted up my desert camouflaged Imperial Guardsmen.
With this pattern I am trying to match up the USMC's desert digital camouflage pattern, called Desert MARPAT. I used a piece of posterboard to make a swatch, but I didn't have a real sample of the camouflage to compare it to, so the best I can do is guess on the colors. Here is a swatch I made superimposed over a digital image of the camouflage.
As you can see the match isn't perfect, but for my purposes it'll do. There may be differences in the colors due to the lighting when the digital image was taken as well, so I'll use that as an excuse for it not being perfect. The base color I used is Bleached Bone, followed by Kommando Khaki, and then smaller areas of Khemri Brown and Graveyard Earth.
Stage 1: I primed the model black, and then painted a basecoat of Khemri Brown over the armor and cloth. Desert Yellow on the base, Tallarn Flesh for the skin, Regal Blue for the glasses, and Chaos Black for the meltagun. Stage 2: Desert Yellow on the armor and boots, Bleached Bone on the cloth, and Tin Bitz on the business end of the meltagun. Stage 3: The difference here is subtle--I applied a wash of Devlan Mud on the armor and boots to tone down the color. The USMC uses a color called "Coyote Tan" for much of their gear. Desert Yellow is close, but too bright to match right, so toning it down with a dark brown wash brings the color more into line. I also used the wash on the face to provide shading. Stage 4: Now onto the camouflage pattern. I painted on irregular blotches of Kommando Khaki on the cloth. I tried to get a large proportion of the cloth, so rather than it looking like Bleached Bone with splotches of Kommando Khaki on top, I wanted it to look more like a 50/50 mix, with it being difficult to tell which color is dominant. I also lightly drybrushed some Brazen Brass on the end of the meltagun. Stage 5: I next put little dabs of Khemri Brown and Graveyard Earth randomly over the camouflage pattern. These colors are less used than the others in the pattern, so I used them both sparingly. Stage 6: Finally I put highlights on the model. I put Desert Yellow on the edges of the armor plates & boots. The Meltagun got a drybrush of Adeptus Battlegrey, with some Chaos Black on the end of the barrel to make it look scorched. One power cable was painted Dark Angels Green with a highlight of Snot Green while the other was painted Regal Blue with a highlight of Enchanted Blue. Indicator lights on th power pack were painted Snot Green and Blood Red. For the glasses I used a mix of Regal Blue and Ice Blue to highlight the bottom edges, and then used dabs of Skull White to provide reflections, and put a coat of 'Ardcoat on them to make them shiny. And he's done!