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, the new yellow Outlook icon is only a fan creation by Thunder_Ruler0.

Why are some icons blue, why are some yellow, and what are those little grey trucks roaming around? Get answers to your icon questions and learn how to control which data sources and types are ...

Google is now updating the icon so that there are no longer four solid color sections. Instead, red bleeds into yellow, yellow into green, and green into blue. It looks more vibrant and colorful.

After introducing on iOS earlier this week, the Google app for Android is now widely getting the new ‘G’ icon with ... bleeds into yellow, yellow into green, and green into blue.