Kerkythea renders the textured and non-textured surfaces as the same colour, and this is the only renderer I've ever used. I know that Sketchup isn't meant to be a renderer, but I'd really like my models to look good in Sketchup.
For the Centaurs I've previously posted to 3d Warehouse (mostly taken down now, and I've lost my account details anyway), I created a ruby script for the gradient between skin and hide, which looks good in Sketchup, but looks terrible if rendered.
Without per-vertex colouring, I need to texture the models, but then they look washed-out in Sketchup, plus a fully textured model is a lot bigger in file size due to all the UV coordinates. The best of both worlds would be if Sketchup displayed textured surfaces with the same specularity as untextured surfaces.