Greetings all! I thought I'd try my hand at this tutorial thing, and demonstrate how I paint the white cloth on my models.

To start with, the two paints I use for my white cloth: White and Fenris Grey. (The irony of using
Fenris Grey on Thousand Sons models amuses me greatly.

)
And the stolid Asim has volunteered to be my model for this demonstration!

First off, base the cloth with Fenris Grey.

Now, here's the trick I use for my blending. First, white paint on the brush like normal. But then, dip the very tip of the brush in the Fenris Grey. The amount of Fenris used depends on how dark you want what you're about to paint to be.

The first few brush strokes! Having both colours on the brush at the same time makes it easier to blend them smoothly - the first few strokes will have a distinct difference between the two colours, and as you continue to paint they'll blend together more. It takes a bit of practice and trial & error, heh.

Continuing to work up the white, still using the fenris-tipped white brush method. Clean your brush between every paint reload!

And more blending. Sometimes I use the side of the brush to add more white on the higher areas of the cloth and avoid the tip with the Fenris on it, then blend the white back into the areas with the Fenris.

The highest areas are highlighted with thinned straight white and blended down into the shadowed areas. Since most of the folds on this particular cloth aren't particularly deep, I didn't leave too much contrast between the lighter and darker areas this time.

And here's Asim with all his cloth finished! Still working on the rest of him, but that's the cloth done at least.

You can, of course, substitute the colours I used with whatever colours you like, though I find having the lighter colour as the main, and the darker colour on the tip to be the most effective, since the darker colour usually goes in the deeper areas, and that's where the tip of the brush is used.
Hopefully this walkthrough made sense and will prove helpful!