AFAIK the first CGraphic is the dropdown bar, and the other two are for the down arrow so you need to add a CGraphic pointer there for the disabled bar, i.e.:
and then you need to add a ImageDropDownWidget::setDisabledItemImage() function, exposing it to Lua and do the necessary things so that the disabled item image is shown instead of the item image if the dropdown is disabled
Andrettin:
https://discord.com/channels/780082494447288340/780082494447288344/894252086420705300