I recall (donkey's years ago) Air UK introduced a midnight blue tail to their fleet of small aircraft. They quickly revised it to white as apparently it made it hard to see the tail at night/early morning (think about winter de-icing activities - this was the UK pre-global-warming).

I think Royal Jordanian also introduced a black tail but put a colour flash (just checked and it is red) across the top to identify the end of the tail.