With last beta: https://dl.dropboxusercontent.com/u/13064071/plantuml.jar
You can now have:
@startuml
hide stereotype
skinparam component {
backgroundColor<<1>> Pink
backgroundColor<<2>> Green
FontColor<<1>> White
FontColor<<2>> Black
}
package "SYSTEM1" {
[ComponentBox] <<1>>
[AnotherCompBox] <<2>>
@enduml
Is this what you are expecting ?
This will be released in next official version.