Hi, this is a tough thing to understand, and many experts even have different opinions.
If I understand correctly, Blue dogs are very rare...they begin as black, with dark pigmentation, almost a blue coloring, then they lighten to silvering in specific areas.
Silver color is more common and usually results in a lighter color.
I always thought that my dogs were blue, but I have been told that they are silver. (Still I am not certain!) This person, who is very wise... :wink: ...told me that, so far, Labs don't carry the dilute gene necessary for blue coloring...so if we have silvering, it is a silver dog (I guess that silver is caused by a different genetic structure than blue)...but she is conducting a study and is looking into this because so many of us claim to have blue Labradoodles.
It takes up to 3 years for the complete cycle, I believe.
There are some good sites for info, here is one:
http://www.canine-genetics.com/pdlcolor.html