FWIW, this is the first step in trying to clean up the Persona dialog and reduce the prominence of Mozilla's branding.

Two of the largest critiques from sites were "Too much you, not enough us" and "I wish I could influence the dialog's color to match my site." Both of those are finally a step closer to reality.

The difference is particularly striking for sites with simple logos / wordmarks: http://people.mozilla.org/~dcallahan/tmp/backgroundColor-tin...

In the screenshot you linked to, the customization changes the URL which is something I would check. With a different URL, I would be suspicious that this is a phishing attempt.

Oh, sorry about that -- that's just the difference between our production / staging servers. Pardon me while I sneak off to Photoshop the URL bar...

Ah, you're working on Persona. I thought you were a 3rd party.

When is this dialog planned to be replaced with browser chrome?

Firefox OS already includes a hybrid native/web implementation in custom browser chrome. I think we're still about a year away from shipping native chrome in Firefox desktop.