In addition to having a modern design, the Outlook icon is yellow. That would be a return to form since the Outlook icon was changed from yellow to blue over a decade ago. As far as I can tell ...

As for actually using the yellow Outlook icon, you may have more luck switching to it for Outlook (classic). The new Outlook is a store app, so customizing its icon is tricky.

A red icon means that you better plug in soon. Yellow means that you’re running low on power, and that (in this build) your laptop is running in its low-power, battery-saver mode. (Microsoft ...