title: E421: Getting color name not recognized in perfectly valid statement
body: <p>I want to change the colors of my parentheses colorized with <a href="https://github.com/kien/rainbow_parentheses.vim" rel="noreferrer">Better Rainbow Parentheses</a>.</p>
  
  <p>The colors are specified like this:</p>
  
  
  
  <pre><code>let g:rbpt_colorpairs = [
      \ ['brown',       'RoyalBlue3'],
      \ ['Darkblue',    'SeaGreen3'],
      \ ['darkgray',    'DarkOrchid3'],
      \ ['darkgreen',   'firebrick3'],
      \ ['darkcyan',    'RoyalBlue3'],
      \ ['darkred',     'SeaGreen3'],
      \ ['darkmagenta', 'DarkOrchid3'],
      …
      \ ]
  </code></pre>
  
  <p>The function changing the colors in the plugin is this:</p>
  
  <pre><code>func! rainbow_parentheses#toggle()
      if !exists('s:active')
          cal rainbow_parentheses#load(0)
      endif
      let afunc = exists('s:active') &amp;&amp; s:active ? 'clear' : 'activate'
      cal call('rainbow_parentheses#'.afunc, [])
  endfunc
  </code></pre>
  
  <p>Since I’m using Solarized I want specific hex colors, so I got this:</p>
  
  <pre><code>let g:rbpt_colorpairs = [
      \ ['yellow',    '#b58900'],
      \ ['orange',       '#cb4b16'],
      \ ['red',    '#dc322f'],
      \ ['magenta',   '#d33682'],
      \ ['violet',    '#6c71c4'],
      \ ['blue',     '#268bd2'],
      \ ['cyan', '#2aa198'],
      …
      \ ]
  </code></pre>
  
  <p>Yet, on restart and turning the plugin on, I get this error multiple times:</p>
  
  <pre><code>E421: Color name or number not recognized: cterm=orange guifg=#cb4b16
  </code></pre>
  
  <p>Even better, doing the :exe done in the function manually works like a charm, like:</p>
  
  <pre><code>:exe 'hi default level4c ctermfg=orange guifg=#cb4b16'
  </code></pre>
  
  <p>Even with concatenation it works:</p>
  
  <pre><code>:let foo = '#cb4b16
  :exe 'hi default level4c ctermfg=orange guifg='.foo
  </code></pre>
  
  <p>What could be wrong?!</p>