I'm at lunch, in between a really busy day, so I'll have to come back to this later, but there was one part I wanted to address.
Daphne once said that both her parents were black and she was black, but she was very light-skinned. Makes one wonder about the delicious rich heritage there. I got an immediate impression of one parent originating from a different country.
The most important part to remember here is that the actress was bi-racial. This is a trend that has been prevalent in tv and movies for quite some time. The less "black" an actress looks, the better and easier it is to incorporate her character into a relationship, friend or lover, with a white actor. I do believe that at times it is a deliberate casting. And while Mykala (sp?) Smith is biracial, she does have distinctive African features. Off the top of my head, the one biracial actress that can most easily pass for white is Jennifer Beals (Bette, The L Word).
So, when Daph declares that everyone in her family is black, she's stating a truth by way of the race that her character was written as. Also, her statement was a comparison to the fact that while Justin's family was white, Justin was gay, making him stand apart from what people saw. Her family...they were just black, and straight (as far as we know). Nothing other than that to make them stand out.