Hello,
Unfortunatly, you cannot... This is hardcoded to black.
However, we build a new beta https://dl.dropboxusercontent.com/u/13064071/plantuml.jar
In this beta, the parameter StateFontColor is now taken into account.
Example:
@startuml
skinparam shadowing false
skinparam StateFontColor white
skinparam StateBorderColor white
skinparam StateBackgroundColor gray
skinparam BackgroundColor gray
state "Any Page" as s1 {
state "Using the text\nsearch input" as s2
}
@enduml
Thank for the report!
