Red/yellow button below microSD slot?

[the7thson]

Hey guys, so my HD2 had a stuck button for some reason and T-Mo sent me a replacement. I noticed that the replacement has a yellow button right below the microSD slot in the back whereas my original one had a red button in that spot. I'm not sure what this is, doesn't seem to do anything.

What color button do you guys have? Any idea what it does or even if it's supposed be an actual button?

Thanks.