Editor color problem
 

Today i open a configuration file for change using vi. But some how i enter any key instead go to insert mode. As a result a word rpm always cbackgroud color is red. When i type any word like rpm its color is red.How can i chnage its previous color.

what configuration file did you open?

I changed sources.list file for apt.

That might be a keyword associated with that file type that vim recognizes, so it uses its "syntax highlighting"

No, the OP accidentally hit the / key, and is seeing the result of colored search results. Just perform a search for a non-existent pattern and the search highlight will off:

/asdflsfdjslf

Mr.C is is absolutely right.

to turn of search highlighting just do the following :nohlsearch
if you want to automate this open ~/.vimrc and add the following

function ToggleHLSearch ()
if $hls
set nohls
else
set hls
endif
endfunction

map <F4> :set hls!<CR>:set hls?<CR>

this way you can turn of highlighting by just hitting F4 key.