Each sector of these piecharts is proportional to the area of the colour on the respective flag. 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.
[Flags analyzed here are Uganda, Ukraine, United Araba Emirates, Vanuatu, Venezuela and Vietnam.]
Next, he combined all the colors together. We see that white and red are the most dominate colors used in flags.