Button or shape border highlights on hover

Hi,

I'm creating a report with some navigation buttons or shapes, clicking takes you to another page.

All well and good. The annoying thing is that when I hover over the button or shape, the outline is highlighted (In this case white, as the background is black), although the border is turned off. Is there any way of turning this off? I've tried turning the border on and setting the colour to black but it makes no difference.