scheme_switcher.vim

function! RandomNumber(limit) 
  let components = split(reltimestr(reltime()), '\.')
  let microseconds = components[-1] + 0
  return microseconds % a:limit
endfunction

function! RandomScheme() 
  let choices = []
  for fname in split(globpath(&runtimepath, 'colors/*.vim'), '\n')
    let name = fnamemodify(fname, ':t:r')
    let choices = choices + [name]
  endfor
  let index = RandomNumber(len(choices))
  execute 'colorscheme' fnameescape(choices[index])
endfunction

let g:total=1
function! SwitchScheme()
  call feedkeys("f\e")
  if(g:total % 15 == 0)
    " update time is usually set to 4 seconds
    " So the scheme would be changed on 1 minute of inactivity
    call RandomScheme()
  endif
  let g:total = g:total + 1
endfunction