Hmm.. all the contemporary Greeks I know are VERY dark-haired. Maybe there have been blondes once, but they seem to have become pretty rare.
The people who inhabit Egypt, Greece and Rome today are not the same people who built those early civilizations. Take a look at any of the early frescos from the early Roman period in both Greece and Egypt (as well as Rome).
The simple fact is that thriving cultures attact multitudes of immigrants willing to perform low-level service functions. Over time, the base reaches a tipping point and the wealth producers move on to a new region, keeping one step ahead of the masses until the cycle repeats itself again.