Why Do Harps Use Red and Blue Strings?

The strings of a modern Western harp may look alike, but they contain a practical colour coordinate system: C strings are usually red, F strings are blue or black, and the others are generally pale or left in their natural colour. The colours are not decoration and do not indicate dynamics. They solve a problem of orientation.

A piano keyboard groups its black keys in twos and threes, allowing the eye to recognise position quickly. Harp strings, by contrast, form a continuous row whose pattern repeats from octave to octave. Counting every string would be unreliable during rapid shifts, arpeggios or passages in which the hands move independently. Red Cs and dark Fs provide two stable landmarks in each seven-note group: count upwards from a red string to the dark F, then continue to the next red C. Colour does not replace touch or hearing, but it shortens the time needed to regain one's place.

The design also shows that an instrument's playability depends on more than its sound-producing mechanism. The pedals alter the pitch state of every string bearing the same note name, the fingers pluck, and the colour markers preserve spatial direction. These systems work together. An audience cannot hear “red” or “blue” in a fast rising figure, but it can hear the continuity, evenness and ease made possible by reliable orientation.

There is a parallel for pianists. Finger numbers alone provide a fragile map; after a large shift, stable positioning also depends on the terrain of the black keys, the harmonic location and the ear. The harp's coloured strings make the principle unusually visible: good playing does not eliminate vision, but gives vision, touch and hearing distinct and appropriate jobs.

https://www.sfsymphony.org/Archived-Pages/Education-Community/Instrument-of-the-Months-archive/harp
https://www.morleyharps.co.uk/how-to-identify-harp-strings
https://manufacturing.dustystrings.com/harps/about-harps/strings-tuning