Every version of Office has its own variation of the application icons. Here is a quick history:

Office 2003 used square “chiclet” icons:

Office 2007 used alpha transparency for unique, non-square, icons and added gradients throughout:

Office 2010 used the solid square of 2003, filled with the icons and gradients of 2007, and added uniform identifying letters for each app (despite the full application suite had 3 “P” icons):

Office 2013 has both a solid square version and a alpha transparency version. The icons are developed direct from the Microsoft Metro style guide, which is simplified icons, but retaining the identifying letters (and yes, still 3 P’s):

When PowerPoint 2013 is launched, one of the immediate reactions is the orange bars and accents in the UI. One of the constants for Office is each application has an identifying color. Looking through the generations of icons, PowerPoint is orange, Word is blue, Excel is green, OneNote is purple, etc. So by the luck of history, the most visual application, PowerPoint, has one of the most offending/conflicting/glaring colors associated with it… I can say, based on the early builds of PowerPoint I looked at, the UI could have been much more distracting.

– Troy @ TLC