Flashing taskbar Icons?

Why do the Icons in my task bar flash a darker color sometimes???? For example, I have my Outlook set to open up 1 minute after I boot up. If I don't do anything with it after it starts up it starts flashing. All my Icons will do this if I open something up and don't do something with them immediately.

All of them?? Which others? I can understand an icon flashing on the taskbar if it wishes to notify the user of, say, an update etc. Can you reset your taskbar settings and switch to a default Windows theme and see what happens/.

Customize Start Menu >Use default settings.