RStudio theme: Modern vs Sky?

Pre-emptive apologies if this is totally obvious, but what is the difference between Sky and Modern for the RStudio Appearance themes (currently running Version 1.1.383)?

My confusion is captured as a gif, below :flushed::


According to the RStudio support site:

However, if you're using a dark pallette, it won't matter:


Yeah, so I definitely should've JFGI'd that one! Thanks, @nick.