Product Options - Selected option/s border colour

I am trying to change the colour of the selected option (an image, not drop down selection) on the product page. Currently it is light grey, then Black when hovering over and then Blue when selected. I cannot find the right values in the css to change. I would like to increase the boarder and change the colour to a more prominent colour when selected.

You'd better give us a link to the page then so we can see the current CSS.