just to throw one more nitch in the figuring, Toni's Lf blacks arent a true Ext black. That's why only the hens are solid black and the males have the red leakage. Even some of the pullets I have hatched have a touch of it. So that coupled with the Cy male adds a bit more to it all.
Like Amanda said, the easiest way to tell is take a silver duckwing and breed to your Cy white. Going off this particular line of blacks will give too many variables
-Extended Black-
"If a chicken has only E, it could look like a gold or silver birchen without the breast lacing, because on its own E doesn't make a totally black chicken!"
Genetics of Chicken Colours pg. 28 by Sigrid Van Dort- David Hancox & Friends
Leakage only means they are missing the proper additional black enhancers to create a full black bird.. Most of these enhancers could be present, but more than likely are not being bred f1 to f1 to make them homozygous and expressed. This is very important.. If you have an almost solid black rooster, you need to breed him back to his daughter to try and get the modifying melanizers to complete the color.. If anyone is breeding black and wants a solid bird, this is my recommendation. The next best would be brother to sister matings.. In theory any black bird can be made with proper melanizers on a birchen, eb (brown) or e+ (duckwing).. If you are missing the proper melanizers like some of the black lines are, you will have to cross back to a bird that has them. Because you can't manufacture melanizers that are not present.. This is why so many lines of blacks never produce good roosters... Extended black doesn't guarantee a black bird.. It just means it has black and white chick down..
here is a link to the pdf that will have the page on extended black for anyone working with them.
http://www.chickencolours.com/Chicken Colour Genetics Basics.pdf
I do think Aubrey is right about them being mixed with the cy male.. You now have possibly E/e+ chicks..