I hope this makes sense, but this is how I understand it :
To get blue eyes, the child needs to inherit 2 blue genes - one from each parent. My dad has blue eyes, my mum brown and mine are hazel so I have one blue gene and one brown. My brothers both have blue eyes so my mum must have inherited a blue gene from one of her parents and passed it on.
My DH has blue eyes so DS1 (brown eyes) must have inherited 1 blue gene from DH and one brown from me. DS2 appears to have blue eyes so must have one blue gene from DH and one from me.
Two blue eyed parents can not have a brown eyed child as neither parent has a brown gene to pass on.
So, Zebra, your DH has one blue gene fron his dad and you must have inherited a blue gene from your mother as, if she did not have a blue gene to pass on, your 1/2 brothers would not be blue eyed. Of course, it may really be down to the blnd haired blue eyed milkman but only you'd know that I have the same jokes as my 2 are blond and both DH and I are dark.
See, clear as mud!!
What I'm not clear on is how shades of green and hazel etc get in on this.