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