Thank you for your reply. This could work, if I know that I will have only two items, but it might be more or less. You think this would be somehow possible?
Oh, wait… I just assumed it was an email address and went down that path (I guess any time I see @, I automatically think email). What is the context of the thing you are trying to highlight? Is it always going to be a @ symbol followed by some text (like a mention)? As Chris suggested and I demonstrated, you really should be able to use BB code to do what you described. That being said, having an example of exactly what you are trying to do would probably help.
Assuming a mention can happen anywhere within a text, you need to find all of the mentions and replace them with a formatted (blue) version of the mention. I can’t access the resource to which @J805 linked, but I am quite certain it will get you down the right path.