Can Diet Coke Cause Brownish Tinged Urine In Diabetic Patient?

Hi, i've recently begun taking Metformin for high blood sugar, I've been on it for a couple of weeks now. Historically, my urine has been quite clear in color, however, tonight it has changed slightly. It's still fairly clear, but seems to have a slight brown tinge as if mixed with a small amount of root beer. My question is, is this a potential warning sign that something is wrong? Also, I drank a diet coke today which is something that I don't normally do, I'm wondering if this may have something to do with it as well. Sorry for the long winded question.