This is a version of https://github.com/altercation/vim-colors-solarized modified to always use true color (24 bit rgb). This means it will work with neovim with the following:
set termguicolors
set background=light " or dark
colorscheme solarized
Normally this wouldn't work with neovim (as of writing) since gui_running is always false during initialisation.
For more info see the original.
All above + it fixes the SignColumn issue referenced here: neomake/neomake#6