Is using different colors for internal and external links OK or what?

I'd like to use different colors for internal and external text links. Please tell me if you think this is a good or bad idea.

I'm considering CSS choices on a new site/web app which will contain article pages that have a lot of internal (same site) and external (another website) linking. By providing a colour identifier the visitor will then know if the link keeps them on site or about to head off to another site.

I've considered box arrow icons but they look unsightly when an article has a lot of external links.

Please if you have any examples of sites/studies which demonstrate this working or failing, it would be great to hear.

Thank you

Matt