Australian Cattle Dog puppies are born white, except for the patches that are their markings/masks later in life. Puppies that will be blue have black markings, and puppies that will be red have brown markings. The white gradually comes in over a number of weeks.
Markings aren’t necessary or even required. If present, however, it’s preferred that black/brown markings not be on the body, just the head (and on the tail is okay, too). The tan that comes in on the legs, chest, head, etc. of the blues over time is correct and the same common pattern that is seen in most black and tan colored breeds.