From my experience with early autochromes they are made from 4 main things potato starch dyed in green,orange-red and inky violet-purple suspended in a (lamp black) substance of pitch mixed with beeswax. the purple dye is as far as im aware Tyrian purple. this combination of dye sets required an additional orange filter to be placed upon the camra lens so the film emulsion would expose correctly allowing a 'correct' colour rendition if that makes sense?