from searching it appears there is a led notification light in place but it does not work right now. Either we wait for samsung/att to send us an update to resolve the issue or we wait for the modding community to provide a rom that does.
BTW. The Nexus One trackball did not have colored notifications when it shipped. The modding community were the first to make this hardware feature work correctly. Google eventually included trackball notification colors in later versions of Android though I believe.