The Silver Penciled Plymouth Rock chicks I got from Dick Horstman are close to 5 weeks old and I can easily tell the males from the females now. I have 7 that are male and 5 that are female. From the start there were around half that were lighter and half that were darker. The lighter chicks are the male chicks and the darker chicks are the female chicks. I am very happy in the health & look of the chicks I received from Mr Horstman.
I was looking at my collection of American Standard of Perfection books today and every edition I have 1910, 1915, 1924, 1945, 1969, 1989 & 2010 has a illustration of the Silver Penciled Plymouth Rocks.