I think this blue line shows there is an over ride on a paragraph style. When I clear over rides it goes away. I have no idea why they occur but think it might have to do with a different child master that I applied with a different text box size.
When I send the document to the printer will the over ride come back?
Yes, it's a paragraph level override.
And no, I don't think it would make any difference to a printer if there are Style overrides, in that it has nothing to do with the printing of the layout. It's really a design-consistency issue.
Thanks Jeff! The article you referenced really helped me understand what was happening. It does seem to be a useful feature, I've located some errant text boxes and some caption boxes that were missing their object style with it already.