The new, top layer on my scoby is always lighter than the older layers. Sometimes I'll see white "scum" forming on the edges. I think it's kahm yeast, but I'm not certain.
I've read that pink or orange mold is the "throw it all out and start over" stuff. I've never (knock on wood) gotten that.
Me either. I drink my homemade kombucha and I have never, ever gotten any kind of buzz from it.
It depends on the strain of yeast that is in the SCOBY ("mother"). If I let mine ferment longer, it just gets more sour. If I let it ferment a reaaallly long time, it's more sour than vinegar. But...