For the color picker, it is “java.awt.Color”
For the date picker, it is “java.util.Date”
For the Enum test, it is “java.lang.Enum”
Where for the Enum I’m not so sure, since this maybe might be like java.lang.Number (superclass) kind of thing …
Tried that already, did not work …
Sorry, lack of (java) development experience and/or imagination 
So where would I declare the class and instantiate the object? Would that be part of the object of the XWiki.WikiMacroParameterClass (like the default value) or ???. Completely lost here …