Tawg,
This page is amazing. Thank you very much for the tip!
I like your idea of putting some blue or violet somewhere on the model. I'll try to think about how to do it. Maybe, as you suggested, adding an object on the base could be a solution. At least, I could add some violet in the shadows of the arms. I used a greenish brown for this model. I could experiment with some violet for the other two witchling stalkers.
On the goggles: I simply didnt paint them. I wanted to have bright eyes like in the original artwork (or maybe I'm just lazy). So, you are right: their color is the same white cream as for the mask (it's not the picture's fault!). I agree with your comment on the green of the eyes: it doesn't match. I first painted the eyes before the rest of the other green parts and used a warmer green as an intermediary color between the dark green and the white. But then, when I painted the metallic parts and the boots, I decided not to use this green anymore. Maybe I could experiment with some violet again for the eyes of the other two guys and come back to this model if this works.
Thanks for your comments! They helped me understand what was bothering me with my work.