Skins
Fifteen ways it can look.
A skin changes the interface, never the behaviour. Nothing you set stops working because you changed the look.
Installing a skin
A skin is a single .skn file. Put it in the program's skins folder and pick it in Options → Interface; no restart is needed.
The skins shipped with the program are: Crystal, First, Freeze, Glass, Light, MediaVista (blue, green, red), Noia, Noia 24×24, Oskar, Phoenity, Starlight, Summer, XP and XP2.
Skins written for older versions usually still load. If one looks wrong, the program falls back to the default rather than drawing a broken window.
Making your own
The Skin Development Kit documents the format. Ask support for the current version.