Hotspots and slices can have a URL and behaviors attached to them, and they can specify an area that changes appearance when the pointer triggers a rollover. You can also change the color of either Web object as it appears on the Web Layer.
Hotspots are merely areas of a single image that trigger a response to mouse movement. Slices can serve the same purpose, but they also cut up an image like a puzzle and then reassemble it in a browser.