One of the best bits of advice for a good render came from a readme when I purchased an Anton Kisiel modelhairstyle. The lights in Poser are too dark with the standard 3-light setting - and are the wrong colour, mostly. Applying this thinking to the texture, if there is not enough light then the colours thicken up and become muddy - giving a loss in quality and detail. I always start with a single light and work up to around 4 lights in total, all either white or grey (no colour). On a head shot I bring the head texture in as a background picture (File:Import:Background) and try to match the skin tone. You can then add very pale colours (not green) to tone the skin.