[sadbot]

This bug has existed for as long as icons with the option for whole or parts has existed, as far as I'm aware. I've never been able to find much rhyme or reason to it, outside of being triggered when loading a saved outfit. Loading a saved outfit that contain part icons, whether it contains all the parts that make up a particular icon or a single one, can cause either the shirt or pants part to no longer appear in the object selection for changing colors. This can be fixed by manually removing and re-adding the part, but this forces you to re-add all the parts of the icon that it comes from which can overwrite other parts of the outfit that you don't want to change.

[Snake]

This happens more often when you use the recolored "Sigrogana Guard" grayscale outfit.

This is apparently due to these grayscale item parts sharing the same name/ID as the colored one, so when the save tries to load that, it fails to.