The Hue UI's browser tab doesn't display the blue-purple elephant as favicon.
Contrary, gethue.com does display it.
The Hue UI's homepage correctly refers to a favicon which is indeed a valid .ico file containing the elephant.
The difference I could quickly find is the mime type being image/vnd.microsoft.icon (on gethue.com) vs. application/octet-stream (on the Hue UI); and accordingly copy-pasting the favicon's address to the URL bar shows the picture in the first case, and offers to download it in the second. This might easily be the culprit.