So that's why Pearl was so salty, she and Rose were actually an item.
Well now everything makes perfect sense and I kind of feel like an ass.
Although Pearl seems to have gotten over it enough to be on friendly terms with Greg, so she's probably much more stable than we all think. At least in some respects.

Also: Sapphire not always having had one eye refers to her design. Rebecca means that when Sapphire was first conceived of, she wasn't sure – Sapphire became one-eyed because Rebecca liked the idea of her being always focused forward.