Straight to your questions:
1) The image map is actually one single image which has some areas defined with coordinates. This being said, to have different colors for different areas you should have the image with the desired areas and colors - since this is an image you cannot set background colors but you should use sa colored image.
2) You can change the background color of the tooltip by using the OnClientShow event. You should reference the popup element there and change the background by using code similar to the one below:
var popupElement = sender.get_popupElement();
popupElement.style.backgroundColor = "Red";
the Telerik team