If you prefer the refreshed Outlook icon in blue, it is also available in Thunder_Ruler0's Google Drive folder. As for actually using the yellow Outlook icon, you may have more luck switching to ...

Updates this week to the Gemini app on Android and iPhone introduce a new app icon that adopts the four Google colors.

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.