Can't Delete a Swatch

Check for placed objects on locked layers. The Find This Color will not show you instances of a colour on a locked layer.

I have run into instances where even after I've deleted the unwanted color from all of my Illustrator and Photoshop files I still can't delete a color from Swatches. As a workaround I found that if I create a new document of the same size as the first one and use the Move Pages option in the Pages Panel pull-down menu to move all pages to a new document the color will not appear in the new document.

As mentioned by @Tilou Jean Paul - you won't be able to delete Swatch if it's used in a linked file.

If you have too many linked files to check - convert swatch to a Spot color and check Separation preview. 

Hi Marianne,

Do you have a linked object (photoshop image or illustrator object) that would itself use this color? If so, you won't be able to delete the swatch in Indesign until you've done so from the other application (Illustrator/Photoshop).