If it's a spot color, you can look at the separations to see where the color is used. If it's a process color, you can temporarily turn it into a spot color in order to see where it's being used.
Another option is to use Object search, and look in turn for the color in fill and stroke. (this won't find it in placed graphics, though)
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Just before deleting a swatch that is bein used somewhere in the document you would get a warning dialog dialog something like...
When you delete an unused swatch you wont get this warning.
To what you have asked, i suggest you file a Feature request at Feature Request/Bug Report Form
However, there may be ways that you can find used swatches using scripting in InDesign.
@find used swatches using scripting in InDesign
do you have one of those scripts on the hand?
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You could do this by creating a custom preflight profile that lists anything that isn't black.
It would then display exactly where the other colours are...