I’m afraid there’s no straightforward way to render Revit models like this in Forge Viewer. The viewer does support high quality (PBR) materials and shaders, but it’s up to the Model Derivative service to specify these materials when converting your designs. And as far as I know, the translation currently outputs PBR materials only for designs coming Fusion 360. Try going to https://viewer-rocks.autodesk.io and look at the materials of the “Fusion Race Car” model.
Alternatively, you could apply custom shaders or materials to your Revit model inside Forge Viewer: https://forge.autodesk.com/blog/custom-shader-materials-forge-viewer.
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