They were not mixed with " Negroid" though and were far from looking like a lightskined madow. The Egyptians were not a fully Caucasiod people like indo Europeans and obviously had their own differences.Cleopatra's sister's mummy showed signs of mixed race and was not entirely Caucasian. Maintaining purity within a single family for 300 years, especially in a land of royalty, is highly improbable. It's likely that they intermarried with high-class families to maintain their dominance in Egypt and prevent overthrow.
They were still majority greek and would've looked as such. The blackest thing their lineage may have possibly touched was nubian blood which ain't negroid but Cushtic. And we all know what happens when cushites intermarry with Caucasiods.