Well its not red...
these guys I wanted to have a dusty desert look, its actually household emulsion, in a cream colour, drybrushed, the pigment density is terrible so pretty translucent and easy to apply.
a pigment can work but seems to take practice.
this is a pigment, applied as a water based wash, all over, left to dry properly, then largely removed with a large brush. The hard part is sealing it, I found an airbrush on a low pressure setting and a thinned gloss varnish worked, took a couple of coats - andthing thicker needs enough pressure it just blew the pigment off
couple more tanks, same process, they go a horrible red colour when you put the pigment on but it mostly comes off.
for a light effect use a satin or gloss varnish under, a heavier finish can be managed with a matt varnish under
guess as with everything its grab a model and experiment, pigments are interesting though.
another alternative if you have an airbrush is a filter
ignore the infantry, the burnt umber is a very thin filter, applied in a couple of coats, could work decently well on the lower third of a marine model in a suitable colour, gets a bit of a ground in look, perhaps to combine with a pigment in some recessed areas (so its not anywhere where parts moving would stop it building up but does get into gaps on packs and so on