You don't need to wear a black coat all the time. And not even a brown coat. Nor a gray one.
You can wear a green coat and look great.
Like this lady in the picture.
See how she stands out in the crowd?
The trick to make something like this work is to keep all the other colors muted. Even better if it's the same color allover.
In her case, she wore black pants, black shoes, a black bag, and black gloves. It also helped that she had beautiful black hair.