Correct. If you're of a lower station, it's a faux pas to introduce yourself to someone of a higher station. Either a mutual acquaintance or someone of the same higher station needs to make the introduction.

For instance, the Ringmaster could introduce you to the Prince or the Prince could introduce himself to you, but you shouldn't start a conversation with the Prince yourself. You should simply acknowledge him with a bow or a tip of your hat.

However, talk to the servants all you like.