I have my own terrain server set up, using custom quantized meshes in very high resolution. Cesium can nicely render satellite imagery onto these meshes.
What I would like to do is turn off the imagery for certain polygons: for the start, streets should be plain grey. Quite probably, more such solid-colored materials will follow.
It is obviously possible to spawn a custom imagery server that would draw grey lines over the satellite images. I did not yet check on the legal side of this (the server would basically proxy Bing map data), but the problem is that drawing solid colors over JPEG bitmaps produces blur and blocky artifacts.
As far as I have found, there is no support for terrain materials in Cesium. (Water masking is kind of a step in this direction, but it is bitmap-based, anyway.) Is there perhaps a branch that could do this, or a project that solved this issue before?