vim-greenisgood works in GUI/true-color terminals, as well as 256-color terminals:
Installation depends on how you manage packages. For example, with Vundle add
Plugin 'rfunix/vim-greenisgood'
to your init file.
Just throw this to your ~/.vimrc:
colorscheme greenisgood
It is important that the flag is set before loading the theme.
Strong inspired in vim-monochrome: https://github.com/fxn/vim-monochrome/