this version is somehow new to me.
it is correct what You write about the North-African influence, but this is true for southern Italy and especially Sicily.
To my knowledge, the fair-hair influence came after the roman empire with the Ostrogoths and Langobards, and continued on a smaller level with the influx from the northern-european contacts through the middle ages. And let's not forget the normans in Sicily
In the antiquity, the whole mediterranean basin was a region of contact and exchange through phoenician and later greek trade and colonization. They should share the same gene pool.
I agree that the dark skinned brunette southern european is a cliche and the reality provides for a good mixture. Nevertheless, it is prevalent.
Now the ocurrence of blonde hair is still a question of research, an acceptable start for the several explanations offered is here in this quite well referenced section
http://en.wikipedia.org/wiki/Blond#Evolution_of_blond_hairand I personally would tend to go with the sexual selection proposed by Cavalli-Sforza starting with the Baltic Region, which also goes with the strong demand for blonde hair in the early principate (for ladies wigs) that was traded from northern europe.
there is also a folklore section here that contains quite a few references about the roman times
http://en.wikipedia.org/wiki/Blond#Folklore_and_mythologyfor which Victoria Sherrow published some conclusive arguments (IMHO)
I think the reason the Prof gave for the blonde roman is actually an authentic one from a roman POV
Edit: there is a reason why my response to the image of the dark-skinned "moorish incursions" gradually changing the original blonde gene-pool seems a bit worked-up. I will send You a PM on this @Poiter50, because I want to make clear that no personal offence whatsoever was intended, however we can't discuss politics here