KB00048 - Can I have different skins on different stickies?

Yes, starting with v7 of Stickies you can. On the Appearance tab in Settings, you can pick a skin which all stickies will adopt, but by clicking any sticky and pressing alt-s, you can pick a skin for just that one note.

To reset an individual note back to the default skin set in Settings, click it and press shift-alt-s.