vim-colors-plain is a duotonic color scheme, the two accents being cyan and pink by default (configurable).

vim-plug does not support installing plugins from sources that do not allow shallow clones (such as git.peppe.rs), i would suggesting installing manually by cloning into your plugin directory or dropping colors/plain.vim into one of the following directories:

• vim: .vim/plugin
• neovim: .config/nvim/plugin