Here are some pics illustrating the only real visual differences I see. In the first pic you can see the exclusion of the wireless channel select switch on the black controller (newer version). You can also see the exclusion of its counterpart switch on the receiver that plugs into the Xbox.
The only other cosmetic difference, aside from the color, is that the original wireless Microcon controller had sideways triangle symbols on the Back and Start buttons, with written lables printed in tiny labels on the controller casing itself. The newer version ditches the labeling and prints "BACK" and "START" directly on the buttons.
I don't know if these details will actually be apparent in any photos available at online retailers, so good luck. It's probably worth noting that I'm almost positive that the crappy handle grips that were included with the first wireless Microcons were prominently advertised on the product packaging. It said something like, "New and Improved Gel Grips!!!" Or something. The Gel grips that came on mine have long been in a landfill, though, and what you see are the (slightly ill-fitting) grips pulled from a wired Microcon controller.
Lastly, I haven't bought an Xbox controller in at least a year, maybe more like two. So, chances are, the controller you get WILL be a version 2. Also, I don't think the version 1 was ever made in solid black, so if you find black ones you're probably golden.