Medium-to-high contrast theme. Its overall presentation hints towards the blue side of spectrum. The most prevalent colours are variants of blue, purple, teal, and cyan.
Equinox comes in standalone light and dark versions (see further info below).
equinox-syntax in Settings > Install > Themes. Or install it directly using the command:
apm install equinox-syntax
Project page: https://protesilaos.com/equinox
Equinox dark version: https://atom.io/themes/equinox-dark-syntax
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.