Logic Puzzles

This is more a reading exercise that a test of logic, I think.

Given the ferry arrives daily, it could be any night anyone leaves. If it arrived alternate days and the guru spoke on Wednesday, then the next to leave, regardless of eye colour, would do so on Friday. But the premise doesn't contain any information that helps in this way, so either I'm plain wrong or the suggestion of a day in the answer is the clue to it being a diversion.

They can't get on the ferry till they've worked out their eye colour. The guru is asking them to know for sure whether they have blue, brown (or another colour) from that one statement.