Wooden standing stones - I don't see why not. Huge timbers were definitely used waaay back at Stonehenge (under the carpark actually) and at the palisaded henges. If there was some 'religious' (or whatever) significance then why shouldn't they have been carved or etched? distinguishing them from more practical defensive or animal-penning fences? Though seahenge isn't carved I suppose. I don't think you could carve a living tree without killing it though (unless you include the growing bark graffiti you see on beeches).

Paint is an interesting idea. Ok they didn't have cans of dulux. But there's evidence that colour was important at some sites (I have got some info on this but not yet written up) - well, Silbury hill's once-blazing whiteness for a start, but also the actual colours of some stones in stone circles. After all, think of those medieval churches you've been in, or the Roman statues you've seen that are apparently minimalist and plain - in fact they were brightly painted once. So with a few mineral and plant-based concoctions, why not on wood, or even stones?