Regarding anti-gas paint used by the BEF, this is another topic where there isn't much literature devoted to. Naturally for best advantage it should be applied in an area that is easily seen. In photos of other vehicle types the front top area seems most popular. One entry states it should be in an area clearly visible to the driver. Colour is usually described as yellow-green, but on the WW2talk forum someone said it was more of a canary yellow.
Taking this into consideration, it is possible these two photos are illustrating just that, but regulations (perhaps from later in the war?) stated the paint should be applied as a blotch to make it less conspicuous, so there goes that supposition. While writing this I just thought of another possible location, inside the cab. This could explain why it is difficult to find definite photos of this marking on the carriers.
Or you can skip the vehicle altogether and have the soldiers wearing the anti-gas paint on their left upper arms.
For your figures, you do have a sound base to work from. Many modelers though have trouble with eyes. I think we all know what they look like as everyday we see faces, but somewhere along the way they tend to get out of scale. Tools and technique are the likely culprits.
For the whites mix a hint of blue and just a tad of brown to dull it down. For the iris, yes it is a circular shape, but the eyelids cover the top, and the bottom lid should just be touching the iris. For this scale even the smallest brush size can make this difficult, so what one has to do is paint in sort of a masking process. The following diagram from a Shep Paine book better illustrates what I'm trying to say.
Basically you lay down your paint in vertical lines to help keep the eyes centered on the face. Then you use a skin tone to cut across to give the eye it's size and shape.
Now if you find this too tedious you can try using a very sharp coloured pencil and apply a stab of colour where the iris is. One thing I hate about very small brushes is they hold so little paint, that by the time you apply it to the surface it has already dried in the bristles.
Only other thing I noticed is avoid dry brushing skin, because it looks, well dry brushed! lol. If you are using acrylics, an application of straight Tamiya thinner might help tone down the stark contrast. For both skin shadows and highlights, build up with appropriate coloured washes.
I hope this helps you as well as anyone else with their figure painting.
regards,
Jack