Material Blueprint doesn't display as expected


I’ve been trying to apply a material to my landscape from World Machine. I’ve imported the height map without any problem and I can apply any material (e.g. wood) to the landscape as well. That all works just fine.

But when I try to create a colored landscape by using the generated color map PNG I get nothing but a grayish background and not the coloring that I expect. I’ve worked on this for quite a while and always end up with the same result. Does anyone have any thoughts? Thanks!