Currently the spot can only have one character, this means it's impossible to set any inline style for it like color, font style, etc; this also means that it's impossible to add an icon, sprite or image as a spot.
I found that placing a sprite in the stereotype may be used to replace the spot:
http://forum.plantuml.net/4076 and
http://forum.plantuml.net/4079 , but it doesn't work with Creole icons.
