Hi @Crs9charles,
There are a few ways to visually highlight a tileset. This post might be of help, it explains how to style clicked tiles.
You’ll need to do a line trace below the mouse to determine what tileset is being clicked on. You can get the hit actor from the line trace, cast it to a Cesium3DTileset, and change the material in Blueprint. You can check out Level 6 of the Cesium for Unreal Samples for an example of using a line trace.
The easiest way to highlight the material is to change the Base Color of the material. On the other hand, if you’re looking to draw an outline around the tileset, that might be more difficult. Will the base color solution work for you?
-Alex