Just reporting a crash in a sandcastle example.
1) go to the Cesium Inspector example in the sandcastle:
2) Click "show frustums".
3)
RuntimeError: Fragment shader failed to compile. Compile log: WARNING: 0:? : '
' : extension directive should occur before any non-preprocessor tokens
ERROR: 0:3: 'gl_FragColor' : cannot use both gl_FragData and gl_FragColor