Riddle: Islanders with Dotted Foreheads
There is an island with 100 women. 50 of the women have red dots on their foreheads, and the other 50 women have blue dots on their foreheads.
If a woman ever learns the color of the dot on her forehead, she must permanently leave the island in the middle of that night.
One day, an oracle appears and says "at least one woman has a blue dot on her forehead." The woman all know that the oracle speaks the truth.
All the woman are perfect logicians (and know that the others are pefect logicians too). What happens next?