The skin parameters for "collections" in sequence diagram, CollectionsBackgroundColor and CollectionsBorderColor, has existed in plantuml.1.2018.0.jar with the command "java -jar plantuml.1.2018.0.jar -language"
However, when I tried to config the border color of collections, CollectionsBorderColor had no effect, but ParticipantBorderColor did change the border color.
A -> C: messages
C -> A: responces
The expect result of C is red border with yellow background.
However, the result of C is green border with yellow background.