Grab color from underlying bitmap and apply it to path objects. The color is averaged all over the path area. Erode parameter can be used to shrink or expand (using negative value) this area. If multiple bitmaps are selected, only one is considered.
see source code on https://github.com/jujumo/inkex_color_trace
I can probably speed up processing (by early crop/downsize of bitmap). Tell me if you think its useful.