Short answer
They grew up with the map rather than being designed all at once. A 1908 combined Underground map was among the first to give each line its own colour; Harry Beck's diagram, designed in 1931 and published in 1933, fixed the idea of colour-coded lines on a schematic, and several lines changed colour in the following years — the Central from orange to red, the Bakerloo from red to brown. Today Transport for London defines each line's colour in a published colour standard, and colours are always paired with line names.
Before 1933, Underground maps were geographic, drawn over the streets. A 1908 map published jointly by the Underground companies showed eight routes, and is described as the first to give each line a different colour and equal visual weight. The colours reflected printing limits and company identities as much as any system: early maps used blue for the Central London Railway, black for the City and South London Railway and red for the Metropolitan. The choice of colour was a way to separate routes on a crowded map of central London, where lines ran close together and crossed often.
Harry Beck, an Underground employee, designed a diagrammatic map in 1931, drawing lines as straight segments at 45 or 90 degrees and spacing stations evenly rather than geographically. It was introduced to the public in 1933 and became the model for transit maps worldwide. On a diagram without streets, colour does more work: it is the main way to follow a route through the tangle of interchanges. Beck kept revising the map, and the line colours with it. In the 1930s the Central line changed from orange to red and the Bakerloo from red to brown, and new lines were added with new colours as the network grew — the Circle line first shown separately in yellow from 1949, the Hammersmith & City in pink from 1990.
Earlier maps were limited by how many colours could be printed and still told apart. Better printing made room for more lines, but also made near-neighbour colours more tempting than they should be.
Transport for London now publishes design standards that include a corporate colour standard and a separate station colour standard for the built environment, so that the colour of a line on the map, on platform signs, on tiles and on trains is specified rather than approximated. That is what turns a set of map colours into a designed system: the same identity has to survive print, screens, enamel signs, ceramic tiles and paint under very different lighting. The standards define colours by reference to colour-matching systems; this page does not reproduce them.
A network with a dozen or more lines cannot give every line a colour that is unmistakable for every rider. Some Tube colours are close in hue or lightness, some are difficult for people with colour-vision deficiencies, and a line name or symbol is always printed alongside. The map also uses other devices — line thickness, double lines for some services, station symbols — so colour is one layer of a system rather than the whole code. Other cities have faced the same arithmetic and reached similar answers: colour for quick recognition, letters or numbers for certainty.
| Line | Earlier colour | Current colour | Change |
|---|---|---|---|
| Central | Orange (1933–1934) | Red | Changed in 1934 |
| Bakerloo | Red (1933–1934) | Brown | Changed in 1934 |
| Circle | Shown as part of other lines; green briefly in 1948 | Yellow | Yellow from 1949 |
| Hammersmith & City | Maroon, then part of the Metropolitan | Pink | Pink from 1990 |
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactModerate evidence
Harry Beck's diagrammatic London Underground map was published in 1933.
Source: Harry Beck's Tube map
FactModerate evidence
An Underground map published in 1908 showed eight routes and was the first to give each line a different colour and equal weight.
Caveat: From a secondary summary; the museum or heritage-body source it cites could not be reached for this review.
Source: Tube map (Wikipedia)
FactModerate evidence
Line colours changed after 1933: the Central line from orange to red and the Bakerloo from red to brown; the Circle line has been shown in yellow since 1949 and the Hammersmith & City in pink since 1990.
Caveat: From a secondary summary; the museum or heritage-body source it cites could not be reached for this review.
Source: Tube map (Wikipedia)
FactStrong evidence
Transport for London publishes a corporate colour standard and a station colour standard for the built environment among its design standards.
Source: Design standards
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.