Shadows of the Sun - The high elves of Darsylon have spent their entire lives reveling in the sun. They understand all of its subtle shades and dapples, its subtle interplays and most of all, its shadows. The elven masters of stealth have perfected their movements under all forms of sunlight, so that even others well-practiced against stealth see nothing but tricks of the light. This does not work on magical forms of stealth.

If elf is outdoors, it is daytime, and the elf in question is hidden/camouflaged, people who can detect hidden/camo have a chance of not seeing the elf on where. They will always see the elf if they walk into the same room. Does not work for invis.

Shadows of the Darkness - I know of two ways to guarantee a dagger in your back. Put it there yourself, or try to find a dark-elf through the shadows at night.

Same, except for dark-elves at night.