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