Possible Duplicate:
.app file appears in red (missing) in new projects with Xcode 4
Since I’ve installed Xcode 4.2, products are in red even if I create an empty application with a template and I Build and Run it.
I don’t remember that this was the default behaviour.
It’s always showing up as red for me as well. It doesn’t really matter, because you get access to the build products through the Organiser in Xcode 4