I think one of the challenges here is that the least used color will be used just once. And there are many colors that appear to be used only once.

I ran the following query to extract color hex strings from CSS files the request_bodies table, and it returned a list of 88,231 unique color combinations. (Note: this doesn’t factor colors set by HTML and JS). The query I ran below, although be warned that it will chew through 770GB of processed data…

SELECT color, count(*) FROM ( SELECT page, url, REGEXP_EXTRACT(LOWER(body), r'color[\s]?:[\s]?#([A-Fa-f0-9]+)') AS color FROM httparchive.har.2017_09_01_chrome_requests_bodies WHERE url LIKE "%.css" ) GROUP BY color

The Regex match is basically looking for color:#FFFFFF , where FFFFFF is any hex string, and spaces are optionally allowed before/after the : character.

Out of 88,231 unique colors, 64,335 of them were used only once! Since there’s a lot of colors tied for last place, I don’t think this can be answered.

BTW - the most common color is #FFFFFF (and it’s shorthand #FFF), which is just white. I’m guessing that I caught a lot of background colors in my search!

Another interesting tidbit I ran into while looking at this is the length of the color codes. I was surprised to see that the shorthand RGB codes are used slightly more than the 6 char RRGGBB versions.