A black mask

I'm looking for a little help with this one.  I photographed a Bushtit (Psaltriparus minimus) in our backyard tonight (28 June 2017).  It was unusual in that it had a black mask — black lores (between the bill and eye) and a black auricular area (behind the eye).  

I know that Bushtits in the southern part of their range (southwest U.S., Mexico, Central America) can have dark masks like this, but I haven't seen one with this coloration in California yet.

Here's the photo:

 

Have you seen or heard of Bushtits with this type of coloration in California?  How common is it?  Any information would be greatly appreciated. 

P.S.  To compare with other photos of Bushtits, here are links to a few older posts:

"Tiny" on 30 December 2016

"Down Jacket" on 8 October 2015

 "That's it!" on 26 August 2013

"The whites of her eyes" on 3 February 2012