The latest upgrade of Ubuntu made my vim colorscheme unusable. I know how to set it manually (:colo evening, for example), but I want to set the default for all
Your .vimrc file goes in your $HOME directory. In *nix, cd ~; vim .vimrc. The commands in the .vimrc are the same as you type in ex-mode in vim, only without the leading colon, so colo evening would suffice. Comments in the .vimrc are indicated with a leading double-quote.
To see an example vimrc, open $VIMRUNTIME/vimrc_example.vim from within vim
:e $VIMRUNTIME/vimrc_example.vim