Mr Khan said that he will launch a programme giving each of the individual lines an “identity” in his manifesto.
Unlike the London Underground, Overground lines do not currently have their own names and colours.
“TfL’s London Overground network has grown considerably over recent years, and to reflect this I’ll launch a programme to name individual routes, giving each its own identity,” he said.
Elsewhere, Mr Khan promised to “recognise and celebrate” London’s diversity.
“We are one of the most diverse cities in the world, yet hugely symbolic parts of our public realm — including our statues, plaques and street names — largely reflect a bygone era, and leave many Londoners feeling that people like them are not visible or celebrated in our city,” he said.
“I have established a Commission for Diversity in the Public Realm to lead work to increase the presence of under-represented groups including women, Black, Asian and minority ethnic, LGBTQ+ and disabled Londoners.”
The Commission for Diversity in the Public Realm was established in the wake of Black Lives Matter protests last summer, during which a statue of the 17th-century slave trader Edward Colston was pulled down in Bristol.
Its aim is to “improve diversity in the capital’s public realm, including statues, street names, memorials and building names” and it currently has 15 members from across the arts and business sectors.