I decided against colour since the chart is 'sehr bunt' already, meaning quite colorful. Colors should be used to highlight the important information so grey fits the purpose better here IMO. Actually I would format them even in a lighter grey tone, but thats where XLs capabilities are limited, only 32 default +16 user defined colors are available and I would not want to change the userdefined ones as they fit me very well in other sheets. (in my XL97 that is, the later versions do have better features there AFAIK)
In any way, the survey's outcome seems to be clear already. The grids win.