I love this tip. For an extremely long time I have always wanted to change the color surrounding my image within Photoshop. The default grey (gray?) color does not always work well while designing. Being able to change that color would be great. Well, you can. This can be very helpful for when you are designing a graphic that you know will be on a certain colored background when in actual use. By changing the background color around your image, you can really see how your graphics are going to look relative to the color that they will be placed on or around. Plus, sometimes we just need a change.
First select the foreground color you like. Then, using the Paint Bucket Tool, (Shift + Click) in the default grey area to change it! I know, I know.. this tip rocks.