On AnyExample.com, there's a quick little tutorial demonstrating how to convert an RGB value passed into a function into the corresponding HTML hex color.

There are actually two functions - one for hex to rgb and the other for rgb to hex (though it's not a far leap to make a wrapper function that handles the value correctly by detecting the format - a string or array). They give the code for both of the functions and a bit of sample code for the PHP it could be embedded in.

The only real place I can think of using something like this is in a web-based graphics application - maybe for color-matching or something. More often than not, though, simple software like Huey for Windows can provide you the same information (and more).

Any other applications you all can think of?