Mac OS X Lion looks a lot different from its predecessor Mac OS X Snow Leopard and one of those differences is the sidebar in Finder and Mail. The sidebar looks a lot different because it displays different elements in Lion and the icon it displays aren’t even in color now.
Open System Preferences and then click on General. Now look for Sidebar icon size in the center section. This option will allow you to alter the size of your sidebar icons from Small, Medium, and Large.
The selection you make will change the sidebar icons in Finder and Mail, but it doesn’t apply to every application. I’m not sure why that is, but that is how it works for now and we’ll just have to live with it until Apple fixes it later.
