From TfL

We’ve introduced new names and line colours across London Overground. Here’s how they look and feel.
London Overground map with new names

Each of the 6 routes that make up the London Overground has its own colour. Follow the right line and line colour for your journey. You can change to other lines where necessary, just like on the Tube.

• Lioness (currently known as Watford Junction to Euston) – yellow
• Mildmay (currently known as Richmond and Clapham Junction to Stratford) – blue
• Windrush (currently known as Highbury & Islington to New Cross, Clapham Junction, Crystal Palace and West Croydon) – red
• Weaver (currently known as Liverpool Street to Enfield Town, Cheshunt and Chingford) – maroon
• Suffragette (currently known as Gospel Oak to Barking Riverside) – green
• Liberty (currently known as Romford to Upminster) – grey
• more  info:

https://tfl.gov.uk/modes/london-overground/overground-line-naming?cid=email_FINAL_TFL1593_LO_renaming_update-London+Overground+line+naming+webpage