Although many in the United States are still waiting for the Lumia Cyan update, most of the focus in the Windows Phone world is shifting to Lumia Denim. Currently, Lumia Denim comes installed on the Lumia 730, Lumia 735, and Lumia 830, with the Lumia 1520 and Lumia 930 slated to get an over-the-air update first, likely starting in the coming weeks.
This morning, a few fan sites began running articles about 'Lumia Emerald' alleging that it is the next firmware update following Denim. For now, I am calling these sightings a hoax for various reasons.
1. Too soon
Lumia Denim and Windows 10 development are the current focus for the Windows Phone teams. Lumia Denim still needs testing on older Lumia phones for its planned rollout, which could stretch into early 2015. The idea that the next update, which is not expected until sometime later in 2015, is out being tested already is a bit hard to swallow.
2. The alleged photo looks wrong
As usual with leaks, there is a photo to claim authenticity. Two things though, one it is very easy to make a screenshot in Photoshop, load it onto the phone and then take a terrible picture. In and of itself, a single photo does not mean anything.
Number 2, the photo cited as evidence seems a lot like the HTC One for Windows. See the above comparison with my HTC One loaded with, ahem, Lumia Denim.
3. No one has heard of it
I have checked with various sources familiar with Microsoft's development plans and they have never heard of Lumia Emerald. Sources can be wrong, of course, or just not know, but this casts doubt on the claim. For myself, this undermines the assertion that it is "getting tested in the wild" as surely many people would now know about it.
4. No codename
Looking at the previous firmware releases, we can see a distinct pattern in regards to public name versus internal codename.
This time, there is no codename, just the final Lumia + COLOR one. Doubtful.
5. Too obvious
Yesterday, many of you in comments were guessing 'Lumia Emerald' as the next iteration. It is somewhat an obvious color (although 'Evergreen' works too). The idea that someone would fake some screenshots with Lumia Emerald, perhaps to troll some sites, seem like something that would happen.
Interestingly, none of these sites claiming to know that it is Lumia Emerald knew about the Lumia Denim name. Maybe even more damaging, they cannot tell you what is in 'Lumia Emerald', just its name. Finally, it greatly helps to have a record of accomplishment on these things before anyone can take such assertions seriously.
In conclusion, the 'E' series of firmware could very well be called Emerald or Evergreen, or something else. For now though, there is no compelling reason to believe any of these stories.