I was tired of the similar looking avatars offered for comments. When changing them in Settings>Discussion>Default Avatar I noticed there was a new one, Robohash.
Robohash has further customisation options but unfortunately they were not available to select in the avatar configuration options of WordPress.
Specifically I liked their “human” set which I think Robohash keep pretty low key as it was only referenced briefly in a single paragraph at the very end.
No point it customising the WordPress core directly because of updates, so instead I created a plugin for others to enjoy: