Philips' solution is to combine two blue and one red element, but use a green phosphor filter to convert one of the blue LEDs to green.

ENGADGET

The first permanent colour photograph was taken by Thomas Sutton who was working with Clerk Maxwell and is a composite of three black and white pictures, each one taken through a red, green or blue filter.

BBC: Pioneering colour photography

Each disc is covered in a transparent plastic coating (either blue, green, yellow or red) which lets daylight filter through.

WSJ: Daniel Buren's Bright Periphery | 'Excentrique(s) Travail In Situ' at the Grand Palais in Paris

They photographed a Scottish tartan ribbon three times, once with a red filter, once with green, and once with blue.

FORBES: GPotD: Maxwell's Tartan Ribbon

Then they developed the pictures and loaded them onto three different projectors, one with a red filter over the lens, one with green, and one with blue.

FORBES: GPotD: Maxwell's Tartan Ribbon

Colour is added by using three separate arrays, each fitted with a filter for one of the primaries red, green and blue that, in combination, produce a full-colour image.

ECONOMIST: Curtains for celluloid