Kinemacolor was the first successful colour film process. It was invented by Englishman George Albert Smith, who started out as a stage hypnotist and something of a charlatan. His initial interest in photography was in showing brief moving picture segments at the end of his shows, but through correspondence with the great George Melies, Smith became quite adept at the mechanics and chemisty of motion photography.
By 1906 he had perfected his Kinemacolor methodology. Films were shot on a single reel using alternating red and green filters, and then projected similarly, at twice the normal rate (ie at 32 fps). Given that this was only a two-colour, not three-colour, process, this was not a full hue system. Reds, oranges, browns, greens, flesh-tones were well represented but yellows were not great, and blues and purples came out as green and murky red respectively. Also, the fact that the red and green frames were alternating meant that you could see a bit of colour mismatch when movements were rapid.
The first test film was Tartans of Scottish Clans (1906) then Woman Draped in Patterned Handkerchiefs (1908), which together run for about 2 minutes.
https://www.youtube.com/watch?v=IbWtviN4BG0
Perhaps the first publicly shown colour film was A Visit To The Seaside (8 minutes long), displayed at trade fairs. Here’s a segment:
https://www.youtube.com/watch?v=akRm4EsXcgk
The first full length film in Kinemacolor was With Our King and Queen Through India, a documentary shot in 1911 and first shown in 1912 at the Scala Theatre in London. Here’s a snippet.
https://www.youtube.com/watch?v=4VCpkplKUf8