Overlay a segmentation over a grayscale volume

I want to visualize the ground truth segmentation overlayed on the chest CT volume. Last time I managed to get a clear visible segmentation overlay (shown below).

However, when I try again today, I do not get the same result. Actually, I forgot the exact procedures that I have taken last time. What I get now is

The segmentation is barely visible. Anyone has an idea how to get the first volume overlay?

Thanks a lot!

You need to make the segmentation a bit larger so that the volume rendering does not occlude it. You can achieve it by lowering the threshold value or expand using margin effect. Making the volume rendering semi-transparent may help, too.