As shown in the picture at the very top, from "Keystone Motel," when Ruby and Sapphire are at war with each other they have red on both sides of the shades with blue straight in the middle. The pictures at the bottom are from "We need to talk" more specifically, when Rose is answering Greg's question.

When Greg asks, "Have you ever loved another human?" Garnet shushes Pearl and listens intently with Sapphire fully in control. (As shown in the bottom left.) Then when she answers with a yes Ruby gets angry and she shows it in the glasses. (Picture in the bottom right.)

This helps my theory of why Greg would see Ruby and Sapphire. Ruby doesn't like the fact that Rose "loves" other people when she's supposed to be with Greg. If Rose was to fuse with someone (bismuth and make Rose Quartz) and decide to be like Garnet that would be the last straw for Ruby.Ruby would get angry causing Sapphire and her to split apart. Thus Greg seeing them unfused.