This makes the numbers go red when inserting, and blue when not.
function JdaInsertEnter()
highlight LineNr ctermfg=yellow ctermbg=darkred
highlight CursorLineNr ctermfg=black ctermbg=red
endfunction
function JdaInsertLeave()
highlight LineNr ctermfg=yellow ctermbg=darkblue
highlight CursorLineNr ctermfg=black ctermbg=blue
endfunction
call JdaInsertLeave()
autocmd InsertEnter * :call JdaInsertEnter()
autocmd InsertLeave * :call JdaInsertLeave()