It's actually really easy to do because vim has a pattern syntax that matches particular column numbers:
syn region Red start="\%61c" end="\%66c"
syn region Blue start="\%66c" end="\%71c"
syn region Green start="\%71c" end="\%81c"
hi Red ctermfg=Red guifg=Red
hi Blue ctermfg=Blue guifg=Blue
hi Green ctermfg=Green guifg=Green