According to the Engadget post, the image comes courtesy of the same leaker who first posted leaked images of what was later confirmed to be the "vivid blue" HTC One.
The image has a time stamp of August 12, which means the gold One—if it is indeed legit—has been in the works for some time, and is not a mere reaction to the unveiling of that other gold colored phone you may have heard about. (Of course, the rumors of the gold version of the gold iPhone have been around since mid-August.)
If the gold One comes to market, it would give users the options of aluminum, black, vivid blue, and red.
This story, "Gold is the new black: leaked HTC One pics hint at new gold color" was originally published by TechHive.