I've always had the same issue with LDView. If you use a colour significantly beyond the main 16 for a slope then you'll get these errors, which I've usually just fixed in a similar way to yourself using scripts. It's not all colours. For example, "tan" and "dark tan" are fine. But certainly the higher ones seem to fail.
There also seems to be a related issued. If you use a slope in a sub-model and colour it with colour 16 (main-colour) and then specify the actual colour in the parent model, the render (if it succeeds at all) will be missing the "bumps" pattern on the slope in the sub-model. But if you directly specify a real colour for the slope in the sub-model then then "bumps" will render properly.
I've always just assumed these to be more LDView bugs, so I'll be keeping an eye on this thread to see if anyone suggests otherwise.
There also seems to be a related issued. If you use a slope in a sub-model and colour it with colour 16 (main-colour) and then specify the actual colour in the parent model, the render (if it succeeds at all) will be missing the "bumps" pattern on the slope in the sub-model. But if you directly specify a real colour for the slope in the sub-model then then "bumps" will render properly.
I've always just assumed these to be more LDView bugs, so I'll be keeping an eye on this thread to see if anyone suggests otherwise.