Update: Birmingham is not “The Mother.” Here’s who is, per the 8th season finale:
The “How I Met Your Mother” crowd is an attentive bunch, and immediately following Monday’s season premiere, fans were scrambling to determine who portrayed the woman at the Farhampton train station.
Strongly identified as Ted’s future wife, given her yellow umbrella, (bass) guitar and presence in the same town as Barney and Robin’s wedding, the woman was shown in more detail than ever before. Fans have previously seen very distant shots of the titular “Mother”–as well as shots of her lower legs–but this was the first to scan directly up her entire body.
Not ready to give her identity away just yet, “Mother” was sure to mask her upper body with a trench coat and cover her face with the tilted yellow umbrella, but still, in terms of setting the wheels in motion for the eventual reveal, this was the most fans have ever received.
For this particular episode, the unidentified “Mother” was apparently portrayed by actress Jennifer Birmingham (http://www.imdb.com/name/nm2138621/), who is credited as “Woman.”
(Update: The IMDB listing for the “Farhampton” episode of “How I Met Your Mother” appears to list several other actors who were neither listed in the post-show credits nor obviously involved in the on-screen action. It is therefore possible Birmingham was listed in error.)
Because the character’s face and full body have not yet been revealed, there is no reason to be certain Birmingham will play the “Mother” when she is actually introduced as a character. In fact, given the savvy of the writing team led by Craig Thomas and Carter Bays, it would be very surprising that the show would let its Mother reveal “slip” in this fashion.
Also, though the pictures suggest it might not be her natural–or only–hair color, Birmingham’s only collection of photos (on iMDB and other websites) only feature her as a blonde.
While a blonde-haired “reveal” would be conceivably possible, especially if the “Mother” is, as many suspect, Barney’s half-sister, it seems to go against a previous revelation on the show.
Back in season four, Ted envisioned how things would have differed had he and Stella, played by the blonde Sarah Chalke, gotten married. Part of that vision involved seeing his kids, regularly portrayed by brunettes Lyndsy Fonseca and David Henrie, as blondes.
Since the kids ended up being brunette, that scene strongly implies that the “Mother,” too, is brunette.
“How I Met Your Mother” has made some continuity errors before, but this would be a particularly noticeable one given its connection to the central story arc.
Though viewers were able to see a silhouette of the “Mother” (presumably Birmingham) from the window of a cab in the final sequence of Monday’s premiere, it was filmed strategically to avoid revealing too much of her face and the color of her hair.*
*Given how intense today’s crop of “Internet fans” is, it would not be shocking if someone uses editing software to make her identity and hair color more apparent.