I do a glaze of sepia over highlighted part of the base.
The most bright part of the base gets the least amount of glaze. As I move closer to the middle line, I increase the amount of glaze, thus increasing saturation and decreasing brightness.
Note that I'm covering the base approximately to the middle line, keeping the shadow area untouched.
If you're unfamiliar with Airbrush Glazing, check out Directional Glazing
article — I use the exact same components ratio described there.
(4) Airbrush Glazing
GW Reikland Fleshshade