Yes, you can sex the silver/gray variety. Take a look at the pics on here: http://www.feathersite.com/Poultry/CGD/Dorks/BRKDorks.html
Scroll to the bottom and they show examples of the different markings between male and female. I do not know about the other colors.
Scroll to the bottom and they show examples of the different markings between male and female. I do not know about the other colors.