Yeah. It does seem counterintuitive, but it’s a result of the uncertainty that what they see is what others do. So they have to communicate a number, and the only way they can is leaving or not each night to count up to it.

I thought about it more and concluded that if the guru had said “I see only blue and brown eyed people” then everyone (but her) could leave the island using the same logic, regardless of how many of each color there was (greater than zero of course because otherwise she wouldn’t see that color). Same for any number of colors too as long as she lists them all and makes it clear that’s all of them and doesn’t include herself.