Medium contrast theme. The most prevalent colours are variants of green, violet, blue, cyan, and magenta.
Oliveira comes in standalone light and dark variants (see further info below).
oliveira-dark-syntax in Settings > Install > Themes. Or install it directly using the command:
apm install oliveira-dark-syntax
Project page: https://protesilaos.com/oliveira
Oliveira light version: https://atom.io/themes/oliveira-syntax
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.