anchor.diff:  
   " Remove color variables
   unlet s:gui00 s:gui01 s:gui02 s:gui03  s:gui04  s:gui05  s:gui06  s:gui07  s:gui08  s:gui09 s:gui0A  s:gui0B  s:gui0C  s:gui0D  s:gui0E  s:gui0F
  -unlet s:cterm00 s:cterm01 s:cterm02 s:cterm03 s:cterm04 s:cterm05 s:cterm06 s:cterm07 s:cterm08 s:cterm09 s:cterm0A s:cterm0B s:cterm0C s:cterm0D s:cterm0E s:cterm0F+unlet s:cterm00 s:cterm01 s:cterm02 s:cterm03 s:cterm04 s:cterm05 s:cterm06 s:cterm07 s:cterm08 s:cterm09 s:cterm0A s:cterm0B s:cterm0C s:cterm0D s:cterm0E s:cterm0F
  
positive.code:     return s:gui03
    elseif a:color == s:gui05
      return s:gui02
    elseif a:color == s:gui05
      return s:gui02
    elseif a:color == s:gui06
      return s:gui01
    elseif a:color == s:gui07
  
negative.code:     return s:cterm04
    elseif a:color == s:cterm04
      return s:cterm03
    elseif a:color == s:cterm05
      return s:cterm02
    elseif a:color == s:cterm06
  