虹色に染め上げるやつ :source して:MyRainbowで有効になります

rainbow.vim

"Wikipediaの色相環の項目の虹色
const s:colors = ['FF0000', 'FF4000', 'FF8000', 'FFBF00', 'FFFF00', 'BFFF00', '80FF00', '40FF00', '00FF00', '00FF40', '00FF80', '00FFBF', '00FFFF', '00BFFF', '0080FF', '0040FF', '0000FF', '4000FF', '8000FF', 'BF00FF', 'FF00FF', 'FF00BF', 'FF0080', 'FF0040']

const s:looper = range(1, 300)

"色付けされた行
let s:painted = 0

function! s:paintline(line) abort
  for i in s:looper
    call matchaddpos(s:colors[(a:line + i) % len(s:colors)], [[a:line, i]])
  endfor
endfunction

function! s:paint() abort
  while s:painted < line('$')
    call s:paintline(s:painted + 1)
    let s:painted += 1
  endwhile
endfunction

function! s:init() abort
  setf text
  for c in s:colors
    execute printf('hi %s guifg=#%s', c, c)
  endfor
  call s:paint()
  autocmd TextChanged * call <SID>paint()
  autocmd TextChangedI * call <SID>paint()
endfunction

command! MyRainbow call <SID>init()