Red files (missing) on Xcode project

This is an easy but tricky tip. Sometimes, when you switch to another branches of the project and go back to the "master", when you open your workspace, the Navigator shows your files in a nice red color (that's intended for when a file is not found but the reference is still there!) so you have a mini heart attack.

Just go to the folder containing your precious *.m and *.h and change the permissions to Read & Write for everyone (don't forget to use the "Apply to enclosed items..." for making it recursive), reopen your workspace and it should make the magic.