- Open your colorscheme.
- Find the lines that start with
hi Pmenu*
. - Edit them to your liking.
If there's no such line in your colorscheme, add the lines below and change the colors to what you want:
hi Pmenu cterm=none ctermfg=White ctermbg=Black
hi PmenuSel cterm=none ctermfg=Black ctermbg=DarkGreen
hi PmenuSbar cterm=none ctermfg=none ctermbg=Green
hi PmenuThumb cterm=none ctermfg=DarkGreen ctermbg=DarkGreen
See :help :highlight
for more.