I've caught up with taking pictures of my Tau (to be posted in future) and started with my Ultramarines. The first squad was going to be my Scouts, but once I had them on the table I realized that I'd never "finished" their cloaks. So, away went the lightbox and out came the paintbrush. Rather than complete the process on all three figures, I decided to leave them in-progress in order to take this photo.
The cloaks were originally just Chaos Black with a dry-brushing of Fortress Grey for highlights. Subsequently, I outlined the blocks of angular camo with Fortress Grey (far left figure), then filled them with more Fortress Grey (center figure). Shading was done by adding VERY small amounts of Chaos Black, darkening as the blocks receded into the folds of the cloaks. Simple, quick, and effective.