[MicroStation V8i] Draped image - export to 3d pdf

I have a digital terrain model (DTM) and an orthophoto. After draping the orthophoto onto the DTM the colors of the image look quite different from the original, with lower contrast. Now I would like to create a 3D pdf, but in the pdf the draped image looks much darker; not satisfying at all.

Is there a way to keep the colors of the original image, so the 3D pdf looks satisfying?

KR, Markus