So for this particular problem, and I suspect it is the same for the other problems, is that the styling for that particular syntax uses the same styling as other actions. For example, the below snippet has "First" and "Second". I believe both of these use the same styling. If I am incorrect, then please let me know how to differentiate.
I think the only way around this is to use inline coloring as shown for Second below. I tried to use custom styling, but I was getting an error when used with !theme cerulean
@startuml
!theme cerulean
:First;
:<color:black>Second}
@enduml
See here for example: http://www.plantuml.com/plantuml/umla/SoWkIImgAStDuL8ioKZDJLL8JYqgpKbDpEFYKb2mSiiiAYwnvkAoiadEpyaliahAIKpEjWjEJSxFIwdbSaZDIm7g1000