Here’s a fun Easter egg in Photoshop CS6 and newer. Press Ctrl K (Mac: Command K) to open up the Preferences panel and choose the Interface tab. Then, under Appearance, you can select the color theme for your interface.
If you hold Ctrl Alt Shift and click (Mac: Option Command Shift Click) on any of the four color boxes, the icons will change from boxes to toast bread. Do this one more time, and the icons will become coffee cups.
This has no effect on the look of your interface, but they are fun little icons to look at!