A 'skin' is a color scheme that is applied to a piece of software. For example, it is possible to change the appearance of Windows software to any number of schemes - it doesn't have to be blue. The term 'skin' is a slang term to refer to these changeable schemes.
Some software comes with multiple schemes or skins. WINAMP, a music player, has perhaps 25 or so. One of the pastimes of college computer folks is to develop customized schemes to reflect school colors, group colors, etc.
I have a hunch hat somewhere out there somebody has developed a skin for WINAMP in our colors. it would be a file that would be downloaded ad aplied to the basic software to change the appearance.