@wizard:
Being a tri, Maggie doesn't like other people or Gossy.
Color has nothing to do with temperament.
Whenever we see each other on walks we both try to grab our dogs so we can talk, otherwise Maggie immediately becomes defensive/aggressive (initially probably just protecting her human) and tries to go after Gossy - one time I was holding Gossy in my arms and Maggie got loose from Carol and jumped at Gossy - got my elbow instead - ouch (no blood TG).
If Gossy and Maggie do not like one another there is little you can do to make them become friendly towards each other. There are, however, ways to have them remain more civilized. Dogs read body language so it is important to pay attention to what you are doing before and during encounters with Maggie and her owner. Are you keeping the leash tight, possibly hunched over slightly, breathing shallowly, or otherwise showing any signs of nervousness, no matter how subtle? If so, this can make your dog wonder what's wrong and put them on alert. If you are not in control of the situation, the dog may try to be and that's where things go downhill.
My recommendation is that both Maggie and Gossy need some basic obedience so they both know how to heel and sit stay. Then when you and Maggie's owner approach one another, have your dogs at heel with a loose leash. Pay attention to your body language. Stand up straight. Take a few deep breaths and relax. When you get close, have your dogs sit-stay next to you but keep a them a few feet apart. Keep the leash short but not tight. This is so you can feel your dog when it moves and reinforce the sit-stay. Stand can be taken an "alpha" position whereas sit is more neutral for the dogs. (It is harder for a dog to "posture" when it is not standing.) Try to position the dogs where they are not staring eye-to-eye. In time you will be able to have Maggie and Gossy in near proximity with one another without an explosive reaction.
Now I've noticed that Gossy gets her hackles up any time she encounters a black or partially black dog.
It is not unusual for a dog to be on alert when it encounters a dog that looks similar to a dog it has had a bad experience with, especially if the dog is downwind and your dog can't smell it. It is also not unusal for the owner to be the cause of the dog's reaction. Sometimes the dog is not concerned until the owner subconciously gives body signals that the dog then acts upon. Watch your own body language. Distraction works well. Have your dog heel and turn quickly and walk away from the other dog, praising your dog if it ignores the other dog. Do this consistently and you and your dog will see positive results.
Whatever you do, avoid the "it's ok" reassurance petting when your dog is behaving adversely. The dog will confuse your actions with praise and assume that you want it to behave aggressively.
Good luck!
but not nasty, or at least not nastier than any other color of B 
It just so happens that a couple of us on this forum have more behavior problems with our tri than our other colors, in fact...my most dog aggressive dog was a brindle..but that isn't a color linked thing...
