CCNA, CCNP, MCSA, CCNA Final Exam, All Answer Test Module With 100/100

I have an image thumbnail with a light colored border which, on mouseover, I want to crossfade to a dark colored border. I'm thinking that the easiest way to achieve this would be to fade in a second div with a darker border over the existing one. Is there a better or different way to fade in a border color change? Thanks.