Is there such a skinparam, ideally one that doesn't also afect other elements of the class diagram? I cannot seem to find it when looking at http://plantuml.com/skinparam
The output of the command:
java -Djava.awt.headless=true -jar plantuml.jar -language
will give you a list of the language elements used by plantuml. Here there is a section skinparameter, have a look through this list.