ORIGINAL: TFF
You can tint your dope, poly, your clear whatever, and bring up the color by layers.
I did a LOT of testing with stains and other colors (coffee) added to polyU and Nelson's clear and never got something I wanted to use (as clear doped linen). The probably with the "layers" approach is that you have to work out how many layers the model really needs first, and then you need to add just enough color so that the total number of layers together create the right color. Another problem is that it tends to "pool" or go on heavier in some areas and so then you get an uneven color...and not in a good way. I'm not saving it can't be done but it would talk an awful lot of testing.
In the PC10 debate, the brown shift has to come from the varnish darkening in the Sun.
My own opinion on this, based on photographing my SE5a model in different light on the same day, is that the "brown/green" issue is a matter of reflective properties in different light. In direct sunlight the model appeared brown, but in open shadow (which tends to have a bluish quality) the model appears more of a darkish green. What a coat of tinted varnish/clear/Poly might add, however, is a pleasing depth to the finish.