Thank you for your quick answer! I found it, but somehow I cannot apply it.
Maybe to explain why: The idea was to make teeth and surrounding bone structure look more like a CT image. I started using 3D Slicer a week ago, so maybe the answer is very easy but right now I’m not able to find my mistake.
It seems you loaded your adtaset one volume per slice, in which case you probably changed the color table of the wrong image. You need to load the volume using the DICOM browser so that it’s a real 3D image.