Highlighting the current line number in vim

There are two groups that determine highlighting of line displayed when &cursorline option is active: CursorLine and CursorLineNR. First is used to highlight the whole line, second for the line number. So to achieve what you want you must

1. Clear the highlighting of CursorLine: just hi clear CursorLine after any :colorscheme and set background= call.

   hi clear CursorLine
   augroup CLClear
       autocmd! ColorScheme * hi clear CursorLine
   augroup END
   

2. Set the highlighting of CursorLineNR if it is not set in your colorscheme:

   hi CursorLineNR cterm=bold
   augroup CLNRSet
       autocmd! ColorScheme * hi CursorLineNR cterm=bold
   augroup END
   

   (better to check whether it is already set in the colorscheme, maybe it will look better in that case).

You can join both autocommands in one of course.

CursorLineNR has been added relatively recently around version 7.3.488.

You want to look at

:se cursorline

and perhaps even/also

:se cursorcolumn