It's been 150 years since Scottish Physicist James Clerk Maxwell showed off the world's first colour photograph at a Royal Institution lecture in London. His discovery is incredible but, technically, it shouldn't have worked.
Best known for formulating classical electromagnetic theory and demonstrating that electricity, magnetism and light are all permutations of the electromagnetic field, James Clerk Maxwell's research in optics led him to hypothesise the three-colour method in 1855. The three-colour method is based around the three types of colour-sensing cones in the human eye: red, green or blue. Maxwell figured that the human eye could be fooled into seeing a full colour picture if three slides of the appropriate colour in the proper proportions were overlaid.
To demonstrate this effect, he and his assistant created the composite picture of a tartan ribbon you see above from three monochrome images, each filtered for a specific colour. The only problem was that the emulsion that he used to capture the monochrome images was really only reactive to blue light. The green light emulsion barely registered anything outside the blue-green spectrum and the red light emulsion did nothing at all. So how did he end up getting a full-colour image? Turns out the ferric thiocyanate he used as the red filter allows a large amount of ultraviolet light to pass through and red-dyed fabrics tend to reflect ultraviolet light as well as red. The red colour he produced was not from the visual spectrum at all, instead he created a full colour image from the ultraviolet, blue-green, blue spectrums.
Maxwell succeeded in creating the world's first durable colour photograph - but for the wrong reasons. So happy birthday, colour photography, you're one of our favourite accidents.