A glass plate was covered with tiny grains of potato starch
dyed red-orange, green and violet in a layer only one starch
grain thick.
Then a light sensitive emulsion was added. Light struck the
emulsion after passing through the colored grains. The
emulsion behind each grain was exposed by light from the
scene that was the same color as that grain.
The result was a full color
Jean-Baptiste Tournassoud,
Autochrome, Early 20th