It's a two stage process (at least):
- Base coat - Vallejo Light Brown (929) which is actually an orange brown.
- Highlight - add Vallejo Light Yellow (949) to taste for as many layers you fancy.
There are a couple of other advantages. The darker base coat creates a better, and much easier to paint, block shape for any area: I think this is a perception issue because the black/light brown boundary isn't as harsh as a black/yellow would be. Finally, the highlight can be applied within the blocked, base coated area without worrying about the edges because leaving some of the base coat showing will create an impression of depth.
I used this technique on the cross on the pennants below:
I also used it on the coat of the camel rider below and the shield highlights: