What is the most used color in the flags of the world?

Red is the most popular color being found on approximately 75 per cent of all national flags of the world. White is present on about 70 per cent of the flags and blue is common on approximately 50 per cent of the flags.

http://www.worldflags101.com/faq.aspx

What is the most popular colour in all the world's flags?

"I did an analysis of national flags (proportions, colours, designs, etc.) for a paper which I presented at the Intentional Congress of Vexillology in August 1999. Red is the most popular colour being found on 74% of all the national flags of the world today, followed by white on 71% of flags and blue on 50%." -- Bruce Berry, 10 Nov 1999

http://www.crwflags.com/fotw/flags/xf-colx.html