The basecoat is olive drab, which color to highlight it? The color is Valejo

I'd mix some yellow shade, maybe goldbrown (Andrea) which is a yellow ochre type of color to the base color and see how that looks. Test it on a practice piece first.

Or Light Olive

........... your question is incomplete !!!!!!!!!!!!!!!!!!!!!!!!!

Take anything (cloth, shoe, wheel.....) and experiment how the color changes when it's indoor, outdoor, near a camp fire.......

I highlight my figures in relation of what is the light source.
I add small amout of different colors in my highlight.

Exemple : there is cadium or naple yellow in a zenithal daylight.
Red, orange, rose in earlier morning (sunset).
Bleu-green-grey under a nice moonlight.
Orange and Red near a fire.........

So your Olive Drab cant be highlighted without more informations.

Never forget this :

THERE IS NO COLOR WITHOUT LIGHT !!

JP

I agree with Jean Paul. The first question should be ' what end result I'm looking for?' Then you go from there

Stephen Mallia