Think about the case of just one person having blue eyes. What would they know and do? 

ah! ok. If that's the case, I can only see one possibility: using water as a mirror! Ahhah

0xbitcoiner

They do NOT know about the 100:100 ratio (only we do).
Furthermore, they do not know that the only eye colors present are blue and brown. Each one must consider the possibility that he/she has an arbitrary color (e.g. green).

Scroogey

science

[Daily puzzle] Eye-land problem

south_korea_ln

I must not be understanding something! When the visitor goes there, no one is there because everyone has left. 