What? I don't think anyone claims them as "white." Some Egyptian dynasties, like the one Cleopatra belonged to, were of non-Egyptian descent (Greek in Cleopatra's case). There were also Persian rulers of Egypt, and Rome ruled it for quite a long time as well, then Arabs, etc.

As to depicting themselves as "dark-skinned," it's pretty well established that they depicted themselves as they were then and are now, as "tan" or "brown," much the same as the rest of the people in the Mediterranean basin and in the middle east.

Edit: I'll add that Egyptians are also a large, fairly diverse people, and categorizing peoples based on antiquated notions of biological "races" is a futile endeavor.