Color option for arrows is not working for timing diagram
WU -> WB : URL
WU -[#red]> WB : URL
Can you please fix all options of arrows.
With version 1.2018.12 (from the plantuml web server: http://www.plantuml.com/plantuml) I get:
@startuml(*) -[#blue]-> [URL1] "First Activity""First Activity" -[#red]> [URL2] "Second Activity""Second Activity" -[#green]> [URL3] (*)@enduml
So I think your version it old (just check with starting plantuml with -version) or that you use the wrong syntax.