The camera pans across from the glasses in Rei’s hand to the two of them together on the floor.
Dr. Nick: Notice the rainbow. I bet that's symbolic, too.
Additional Commentary
Kendrix: Note that Rainbows are present in Rebuild as sigh of an angel being defeated; by beginning his connection with Rei, he sort of 'defeated' the second angel. But what's it doing in the original? Well, the rainbow is in the story of Noah, a symbol of a promise/bond between god and humanity. This is the beginning of a bond between a human and a divine being that will eventually influence the fate of humanity.
thewayneiac: Aren't you probably overthinking the religious symbolism there?