Using a list of countries generated by The World Factbook database, flags of countries fetched from Wikipedia are analysed by a custom made python script to calculate the proportions of colours on each of them. That is then translated on to a piechart using another python script. The proportions of colours on all unique flags are used to finally generate a piechart of proportions of colours for all the flags combined.
Embedded on top is a screencap of a portion of the display, alphabetically arranged (Afghanistan, Albania...); the original at the artist's website will display the name of the country when a mouse is passed over the pie chart. The larger pie chart on the bottom is a composite of all the colors from all of the flags.
Via The Life and Times of Michael5000, who notes that the color violet/lavender/purple is notably absent from world flags (as is gray).