ENH: Change label opacity with the foreground opacity
ENH: Change label opacity with the foreground opacity

KitwareMedical/VesselView,matthieuheitz/VesselView,KitwareMedical/VesselView,matthieuheitz/VesselView,sumedhasingla/VesselView,agirault/VesselView,matthieuheitz/VesselView,agirault/VesselView,agirault/VesselView,sumedhasingla/VesselView,sumedhasingla/VesselView,KitwareMedical/VesselView