for polygons which are extruded the colors of all sides of the model are little bit different, which looking grat. It feels like shining. see picture https://picload.org/image/wplwwcc/2d.png
if i have complex models, which polygons are describe one by one, then there is only one color with no shining effect. see picture https://picload.org/image/wplwwcp/3d.png
The best solution would be to represent your building models using glTF and use our new 3D tiles specification to load them. To learn more about 3D tiles, see this forum post: https://groups.google.com/d/msg/cesium-dev/tCCooBxpZFU/7hxT_E4pGgAJ
I can’t think of any workarounds using polygons other than to just use your first approach using extruded polygons.