Well, it's rather simple.

In order to make TB recognize your family members, you place all of them in the same address book group, let's call it 'family'.

You want to make their mail in a different color, so you've got to create a color group. That can be done via:
Message -> Colour Group -> Edit Colour Groups

Now you create a filter, make it an incoming filter with the condition:
Address groups: Family - contain: sender
As action you set:
Set message colour: ....

There are other ways to keep your family post separated from the rest. I've created a dedicated folder for it. And not only did I create an incoming filter that moves family mail to that folder, but I've also created an outgoing filter that moves my messages to the same folder when all recipients are in my family address book group.