Undercoat white, wash a couple of times with a heavy black wash. Pick out details such as unit markings in white, then wash again with a medium black wash.
I would perhals do one less wash of black on either the armour or fatigues so that they are not quite so monochrome. Looking at the first picture, the fatigues look darker than the armour, so I might give the armour less heavy washes.
For browns and so on, I would wash with a mid-yellow then hit with whatever the darm-mid brown wash is called these days, being careful to use a damp, clean brush to clear the wash from the raised surfaces as much as possible and flush it into the recesses.
For the visors I would use an ink of an appropriate colour to give it a glossy look. If you repaint the visor white (if you need to - depends how careful washing the model black you were

), then hit it with a sepia or brown wash, using a damp clean brush to flush the wash clear of most of the lens and concentrate it around the edges before inking it, you should get a nicer, dirtier looking lens.