Logic for entering/leaving a pane. Provides a column for active pane.

pane_logic.vim

" Logic for entering/leaving a pane
function! OnWinEnter()
    if exists('w:initial_cc')
        let &colorcolumn = w:initial_cc
    endif
endfunction
function! OnWinLeave()
    if !exists('w:initial_cc')
        let w:initial_cc=&colorcolumn
    endif
    let &colorcolumn = 0
endfunction

augroup BgHighlight
    autocmd!
    autocmd WinEnter * call OnWinEnter()
    autocmd WinLeave * call OnWinLeave()
augroup END