Is calling an African American person "colored" a racial slur?

I am not African American, nor have I ever used any racial slur towards any race, but I was curious because someone I was talking to today referred to black people as colored. It offended me, b/c I have several friends who are black, and I don't see them as "colored", just darker skinned. IMO, someone who is colored should be just that...colorful, and I don't know about you, but I've never met anyone looking like a box of lucky charms. Any thoughts? I'd really like to know if it is a term that African Americans take offense to....just out of curiousity.