In the late 1900's I started reading an English language paperback novel where some of the children being born had a luminous patch on the forehead, and a wax like substance behind the ears. Eventually enough of these children were born that they began meeting each other. When they did, the luminous patch began changing color. The color changes progressed into a rapidly flashing fluctuation of color. They were communicating visually instead of aurally. I remember neither the title nor the author.