Q: "You can be reached by iMessage at" the email is grey colored. Why and how can I use this email to receive iMessages?

When trying to select an email address to receive iMessages I can't seem to select an email. It's in a light grey color. I can't figure out how to get it to be in a normal color so I can highlight it to use for iMessages. It's my son's iPod Touch and his iPod Touch is hooked up to my account. Does this make a difference. I have most of the iCloud stuff turned off so we don't have to share a lot of stuff.