You need to load the NIFTI file (shift it over the 3D Slicer windows) and then shift the segmentations over the Slicer window, but load them as segmentations
Unload all.
Load the ct.nii.gz first as a volume.
Then rename all organ segmentatons to xxx.seg.gz and reload them.
Then create a Folder “Segmentation” in your scene.
Push all segments into that folder.
Open the Segment editor.
Give every segment a different color.