use __accent to better differentiate between a real group.

autoload/airline/builder.vim

@@ -24,7 +24,7 @@ function! s:prototype.add_section(group, contents)
   endif
 
   let contents = []
-  let content_parts = split(a:contents, 'airline_accent')
+  let content_parts = split(a:contents, '__accent')
   for cpart in content_parts
     let accent = matchstr(cpart, '_\zs[^#]*\ze')
     call airline#highlighter#add_accent(a:group, accent)

autoload/airline/init.vim

@@ -68,7 +68,7 @@ function! airline#init#bootstrap()
         \ 'accent': 'red',
         \ })
   call airline#parts#define_raw('file', '%f%m')
-  call airline#parts#define_raw('linenr', (g:airline_symbols.linenr).' %#airline_accent_bold#%3l%#__restore__#')
+  call airline#parts#define_raw('linenr', (g:airline_symbols.linenr).' %#__accent_bold#%3l%#__restore__#')
   call airline#parts#define_function('ffenc', 'airline#parts#ffenc')
   call airline#parts#define_empty(['hunks', 'branch', 'tagbar', 'syntastic', 'whitespace'])
 endfunction

autoload/airline/section.vim

@@ -11,7 +11,7 @@ function! s:create(parts, append)
 
     let val = ''
     if exists('part.accent')
-      let val .= '%#airline_accent_'.(part.accent).'#'
+      let val .= '%#__accent_'.(part.accent).'#'
     endif
 
     if exists('part.function')

t/builder.vim

@@ -40,13 +40,13 @@ describe 'active builder'
   end
 
   it 'should replace accent groups with the specified group'
-    call s:builder.add_section('Normal', '%#airline_accent_foo#hello')
+    call s:builder.add_section('Normal', '%#__accent_foo#hello')
     let stl = s:builder.build()
     Expect stl == '%#Normal#%#Normal_foo#hello'
   end
 
   it 'should replace two accent groups with correct groups'
-    call s:builder.add_section('Normal', '%#airline_accent_foo#hello%#airline_accent_bar#world')
+    call s:builder.add_section('Normal', '%#__accent_foo#hello%#__accent_bar#world')
     let stl = s:builder.build()
     Expect stl =~ '%#Normal_foo#hello%#Normal_bar#world'
   end

t/init.vim

@@ -28,7 +28,7 @@ describe 'init'
   end
 
   it 'section c should be file'
-    Expect g:airline_section_c == '%<%f%m %#airline_accent_red#%{airline#util#wrap(airline#parts#readonly(),0)}%#__restore__#'
+    Expect g:airline_section_c == '%<%f%m %#__accent_red#%{airline#util#wrap(airline#parts#readonly(),0)}%#__restore__#'
   end
 
   it 'section x should be filetype'

t/section.vim

@@ -32,7 +32,7 @@ describe 'section'
           \ 'accent': 'red',
           \ })
     let s = airline#section#create(['hi'])
-    Expect s == '%#airline_accent_red#hello'
+    Expect s == '%#__accent_red#hello'
   end
 
   it 'should parse out a section from the distro'