I think the earthen look is due to the fact that I use for browns in most cases either artist acrylic paints – or artist water colour paints, nothing can beat in my view paints like burned umber, natural umber, raw Sienna, burned Sienna, etc.
the basic approach is -
Base colour – white acrylic spray paint – GW skull white which never had let me down.
Then pre painting, in case of redcoats with artist natural umber in sort of a light glaze – faces and hand with a wash of burned umber.
For figures with dark blue coats – I use a deep violet (Mix of crimson and prussian blue, artist acrylics)- this gives me shades in deep recesses and definition so details pop out very well.
Next stage is to apply a base colour of the desingated part of the uniform.
Two options, work well for browns, blacks, dark greens, dark blue – the easy approach
This base colour is painted much lighter than the desired outlook, for dark blue – a light blue, due to colour theory in a warm colour, leave out the deep shades and let the pre paint.
After it has thoroughly dried apply a light glaze of a dark colour – a very dark blue – I use for that – artist water colours – in combination with a flow medium (acrylic paint retarder with about 5 to 6 parts destilled water).
This is shading by itself, then with a moist tip of the brush – take off paint were lights are desired (on the above miniatures this was used for shoes, gaiters, cartridge box, hat, hairs, ribbons for the queues, cockade, bread – bag, blanket roll.
For some colours it doesn't work, alas white, red, yellow, flesh, there I have to use the usual layer method – but I also don't overpaint the most deepest shades and leave the pre – painted recesses (this layer is darker as the desired final hue), then I usually use a light glaze as well with artist water colours, to give depth to the colours, then unfortunatly active highlighting – I usually use the base colour I used before I had applied the wash and go light (in case for the overalls) – in case I desire, costs more time, but I don't have found a way yet how to paint those colours the easy way.
Why water colours for the glazes (other then the pre painted one which has to be acrylics), I always am able to take away paint with a damp brush, also in case a glaze is smudging too much the recesses and I want a strong shade.
So black, is really easy, white – more investment in time.
By the way for the light glaze on the red coats I used crimson and mixed in a bit a dark green, by that the depth of the colour is much enhanced – I used once also just dark green on a red coat for experimentation, not a bad effect, but the shades appeared almost black, which I don't desire.