I used viewer.scene.primitives.add and ClassificationPrimitive to add multiple geometries, suggesting that all geometryInstances must have the same color properties, then I changed to viewer.scene.groundprimitives.add, showing the same error.
Thanks for reporting this! Can you provide a little more info here? Like what error exactly are you getting?
If you can recreate this issue in Sandcastle (https://cesiumjs.org/Cesium/Build/Apps/Sandcastle/) that would be super helpful. Just click on “Share” and paste the link you get here. That’ll help us a lot in debugging and fixing this.