This is Blue, he's an Australian Cattle Dog (aka Blue Heeler), they are a very alert dog, don't really like strangers all that much and very intelligent.
He lives with two little female 3.5kg Silky Terriers that totally and utterly lord it over him.
Great looking heeler. Our little girl Indigo (Indi) is a little over a year. She's lost most of the "blue" as she was very dark at birth. Both of her parents are red heelers. Like you said, she is very protective of our family.