becoming the leader

Question
I am currently the proud owner of a beautiful 6 month old, red and black, male German Shepherd. He has been a wonderful dog at home, usually well mannered and follows me like a shadow. When we are home, he is the perfect dog. Rambunctious at times, but hey, what puppy isn't? But outside the home, I find I'm beginning to have trouble controlling him. We have perfected loose leash walking and have been working on heel. But as soon as he sees another dog or a person he wants to greet, he will try to pull me in that direction. Or when we have guests come over, he's always jumping and will ignore my commands until I force him into a sit. We have been taking obedience classes so his jumping and other mild behavior issues have been steadily decreasing. But from what I understand, I am still lacking dominance. If he barks, it takes me awhile to get him to stop. And even if he's sitting perfectly at my side, he'll get up and try to pull me to a dog or person he wants to greet. I already feed him after I eat, make sure that I walk through doors before he does and manipulate attention as best I can (only giving him attention when I want to, not when he asks for it). But it seems I am still lacking that dominance.  I want to be able to tell him to settle down once with a stern look and have him stop barking. I've seen my obedience trainer do it to his dog and it's amazing! So I was wondering, what else can I do to position myself as the alpha in our pack? What else do I need to know and what else can I do to be the one in unquestionable control?

And just one thing on the side. He's been loosing his black puppy fur and getting in his red, but when can I expect him to get his full adult coloring by?

Thanks!

Answer
Obedience lessons should help.  The eye contact can be a powerful tool.  Check http://www.dogbreedinfo.com./topdogrules.htm  he still should be young enough for some of this:

''Elevation for small puppies:  Sit on the floor and gently put your hands around your pup's middle, below his front legs, and lift him up.  He is facing you.  Hold him for 15 seconds.  Repeat until he no longer struggles.  If he is past 10-12 weeks, lift his front feet off the ground, but don't pick him up.  

Cradling for small puppies:  Hold your puppy gently on his back, as you would cradle a small baby.  If he struggles, hold him firmly until he quiets for 10-15 seconds.  With larger pups, you can do this as your sit on the floor, with your pup between your legs.

Quiet lying down:  Place your pup on the floor on his side, with all 4 legs pointing away from you.  Use your hands on his neck/shoulder area and middle, to hold him in this position.  When he is quiet, praise him.  Lengthen the time that you keep him quietly in this position.  When he accepts this position well, handle his paws and muzzle, while keeping him quiet.''

The quotes mean this isn't my original work.  It is copied from my Puppy Raising Manual.  I have long used these or minor variations of them, and they are very effective.  You may want to give him a belly rub while he is on his back too.  Helps bonding.  There is a big difference between him rolling over and demanding a belly rub, and you choosing a time to roll him over and rub his belly.  The latter cements your place as pack leader.