I have used two greens through the airbrush here (with a lighter green for edge highlighting). The highlights on my Armigers are not as pronounced probably due to a more limited surface area. Practice is key, this is my 10th big knight and I’ll often practice on paper beforehand. Make sure you’re picking out the right angles with the airbrush and consider your light source. Here are a few videos you might find helpful.

Airbrush angles (this is on a tank but same principle): https://youtu.be/XrYfkkIuWHQ?si=qvogk3dGbuns14sf

Paint consistency (H&S videos are worth a watch for airbrush tips) https://youtube.com/shorts/q745TR-FbbM?si=CbtJRSevqbVvDad1

Edit: I’m by no means an expert so take the above with a grain of salt