According to color theory. as I understand it , a very transparent glaze of the complimentary color should mute the yellow. That's purple (red+blue). It might take more than one coat, so go slowly, watch the results, and adjust from there.
I'd mix 1 part of purple from the tube with about 10 parts glaze medium, put a little on my brush and blot until almost dry, and try it in a place that does not show too much. Let it dry and see what happens. I'm sure it will mute the yellow, but not sure what it will do to the khaki. You might need several coats to mute the yellow sufficiently. You might then need to glaze the khaki with another color to bring it to the hue you want.
If you still have some of the original color, put it on an old figure you don't care about and practice until you get he result you are looking for. You can short cut the dry time by using a crock pot or 100watt bulb to dry the figure overnight. Be sure it is dry completely to evaluate the results.
Hope this helps.
