Try baby wipes.
They should do it if it's muck, but the it could just be discoloured... if that's the case am not sure.
@TM started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
Try baby wipes.
They should do it if it's muck, but the it could just be discoloured... if that's the case am not sure.