Cesium渐变色3dtiles白模（视频）

参见：
https://mp.weixin.qq.com/s?__biz=MzU2ODYzNzc4OQ==&mid=2247486233&idx=1&sn=51fc740b4e43fe0283b3ab8c0ce00f93&chksm=fc8bab2bcbfc223dcd1724f8758ad83091ea44ca2368cbcbaa3a49c490a7734fd1b1694e182d&token=1138292218&lang=zh_CN#rd