Properly figure out (n)vim's color mode

plugin/interestingwords.vim

@@ -190,20 +190,22 @@ function! s:markRecentlyUsed(n)
  call add(s:recentlyUsed, a:n)
 endfunction
 
+function! s:uiMode()
+ " Stolen from airline's airline#init#gui_mode()
+ return ((has('nvim') && exists('$NVIM_TUI_ENABLE_TRUE_COLOR') && !exists("+termguicolors"))
+ \ || has('gui_running') || (has("termtruecolor") && &guicolors == 1) || (has("termguicolors") && &termguicolors == 1)) ?
+ \ 'gui' : 'cterm'
+endfunction
+
 " initialise highlight colors from list of GUIColors
 " initialise length of s:interestingWord list
 " initialise s:recentlyUsed list
 function! s:buildColors()
  if (s:hasBuiltColors)
  return
  endif
- if has('gui_running')
- let ui = 'gui'
- let wordColors = g:interestingWordsGUIColors
- else
- let ui = 'cterm'
- let wordColors = g:interestingWordsTermColors
- endif
+ let ui = s:uiMode()
+ let wordColors = (ui == 'gui') ? g:interestingWordsGUIColors : g:interestingWordsTermColors
  if (exists('g:interestingWordsRandomiseColors') && g:interestingWordsRandomiseColors)
  " fisher-yates shuffle
  let i = len(wordColors)-1