It seems to be some problem when using skinparam for setting the border color of a styled package (frame, folder, etc) when the package contains other elements. I give an example to demonstrate:
@startuml
skinparam FrameBorderColor pink
frame "First frame" {
[test]
}
frame "Second frame"
@enduml
The above example will draw correctly the second frame (which contains nothing), but the first frame will be drawn with a black border. In fact, the color of the first frame border can be changed by setting the PackageBorderColor:
@startuml
skinparam PackageBorderColor purple
skinparam FrameBorderColor pink
frame "First frame" {
[test]
}
frame "Second frame"
@enduml
It seems that the same is true for other skinparam options, like the font color. Some options though, in particular the background color, seem to work correctly.