Question about Suits and Overcoats?

Being from the South (yes, I capitalized the 'S' in South on purpose), I rarely see cold weather unless I am on vacation.  Also, the fact that I am a computer nerd by trade, means that I rarely have to wear much more then pants and a short sleeve shirt (and no, I dont work for the Geek Squad). 

That being said, I have an interview tomorrow in Manhattan.  I own a black suit and can borrow a khaki overcoat from my father-in-law.  Does my suit and my overcoat need to match?  Would I be better just not taking the overcoat since it is a different color then my suit?

Thanks for any input!  You guys are the best!

REM