Just have to say this

Anyone else find that Ethiopia and Barbarians are exactly the same when looking to attack/save a worker/settler? Is there some difference I am missing to tell them apart before the tool tip warns me of war?

Three solutions exist:

1) Download mod that lightens the green in Ethiopia's colors.
2) Have military unit selected, hover over mystery unit. If you see combat calculations, that unit is not your friend.
3) Exterminate Ethiopia to remove all possibility of confusion.

I had also faced the same problem, they look so alike!

They aren't quite identical, but you really need both a barb and an Ethiopian unit in the same screen shot to tell the slight difference in shade color. (Ethiopian is one shade darker, and actually looks a bit more menacing)