RN, that's fair enough. I wasn't trying to offend you or anything. I just wanted to make it clear that there are many subgenres that fall under the umbrella of "Metal".
As for dressing in black, P.O.D is generally put under the "nu metal" label, and they wear whatever colours they want, not just black. Same for Metallica- they have been known to wear other colours. I'm sure there are other examples too.
As for all metal sounding the same, I guess that's subjective, and it may sound the same to you, but there really are big differences between subgenres, and there should be (but aren't always, unfortunately) between the bands that make up those subgenres. That's the same for any major genre though.