Actually, I think he proclaimed himself not a Dark wizard because he knew he'd get in trouble for it. Again, I agree with Mistletoe -- he's an ambitious Slytherin, first and foremost. He goes for whoever can make him stronger, and I bet if Voldemort ever weakened, Lucius would rush into to take his place. He came back to the Light because the Dark was in disarray. He returned to the graveyard in GoF because the Dark Lord was on his way up again.
I think he might believe that what he's doing is the right thing, that muggles really do deserve to die, but he made such a big deal of telling Fudge and the others that he was not a 'dark wizard' that it's obvious he knows that the Death Eaters are evil.
Whatever you want. I think the resemblance between him and Draco is in their colouring, not hair length. After all, Draco's hair changes in every movie. :)
This is weird, too, but does Lucius have short or long hair? It never mentions the length of his hair in the books, but it does say he resembles his son. His hair is long in the films, and I can't imagine it any other way, but I've seen it depicted as short in fan art.
Only one other canon fact: Remember that he uses bribes. He has a lot of influence over Fudge through charitable donations to St. Mungo's and the like (if he gives to charity, he can't be evil, right?). And Fudge treated the Malfoys to box seats at the Quidditch Cup.
In short, Lucius is an enigmatic character, and we don't know much about him, other than the obvious. Does anyone have any suggestions for writing Lucius?