Atomic-blonde is a SourceKit-based syntax highlighter for the swift language. Unlike highlighters powered by regular expression grammars, atomic-blonde calls into your swift compiler installation to provide perfect, accurate syntax highlighting. The highlights you see in atom are the same ones the swift compiler sees.
Atomic-blonde requires a swiftenv installation to work. The version of swift atomic-blonde uses is the same version of swift (global or local) that swiftenv is set to for a particular project.