Why are Romans blond and Sicilians brunette?
Actually it's a tad more complicated than that. Assuming you're
referring to modern Romans, they generally reflect a mix of all of
the various phenotypes that one would see throughout Italy as many
people from northern and southern Italy have migrated there over
the decades (and centuries too probably). The ancient Romans were
much like the modern Italians, some were lighter and others were
darker but there was probably a general prevalence of brown
hair/eyes, brunet white/light olive skin tone, and sharp facial
relief (again like today's Italians). As for Sicilians down in the
south, there's tremendous variation in the appearances of the
people due to the many conquests and settlements of various
European and Mediterranean peoples over the many centuries. While
Sicilians tend to be darker than most other Italians on average,
one can see many individuals with blond or red hair and/or
blue/green eyes throughout the island because the Viking-French
Normans conquered and ruled Sicily at one time. Many Sicilians also
have fair complexions for an island right in the middle of the
Mediterranean as well, which is also partially due to Norman
genetic heritage. Fairer coloring could also be attributed to the
many northern Italian immigrants who came to Sicily in the wake of
the Norman conquest with the purpose of establishing Catholicism in
Sicily at the expense of the Greek Orthodox and Arab Muslim
communities. The Arab Muslims had ruled and settled in Sicily prior
to the Norman era, and like the Norman invaders, most of the Arabs
were men who married local Sicilian women (themselves primarily of
Greek ancestry dating from large waves of ancient Greek and
Byzantine Greek immigrants mixed with indigenous Siculi, Sicani,
and Elymi populations in Sicily). Many other native Sicilians
converted to Islam and became culturally Arabized in order to
escape persecution for being Christians, though a large Greek
Orthodox Christian community remained throughout the period of Arab
rule right up to and into the era of Norman rule, when Latin speech
and Catholicism slowly supplanted all other cultural influences (c.
1100-1200 or so). Thus, of all the Italians, Sicilians are the only
ones (perhaps Calabrians as well) with a notable contribution of
genes from the southern and eastern shores of the Mediterranean
(North Africa and the Levant). This is why one sees some Sicilians
with such traits as black curly hair, dark eyes, olive skin, and
Semitic features (i.e. larger nose, fuller lips, large eyes,
heavier eyebrows, etc.). Then there are the many Sicilians with
classically Greco-Roman features, straight to wavy brown/dark brown
hair, hazel/brown eyes, and brunet white/light olive complexions,
who look more like the standard southern Italian or Greek. This
type is the most common. Lastly, there are the Sicilians with
lighter hair, blue/green eyes, and fair complexions, which would
come from Norman, northern Italian (i.e. Lombard), or possible
French ancestors. Of course, you can also see Sicilians who look
like they could be a mix of two or more of the above combinations.
For example, I've seen redheaded Sicilians who tanned well and had
classically Greco-Roman features. Likewise, I've seen dark-haired
green-eyed Sicilians with Semitic features, and so on and so forth.
As someone with both Sicilian and northern Italian (Florentine)
ancestors, I know quite a bit about the variety of looks one sees
among Italians. My Florentine maternal great-grandmother was blond,
blue-eyed, and with sharp facial features so commonly seen in
Italians. Contrarily, my father is 100% Sicilian and my relatives
on his side range from blond and blue-/green-eyed to
Semitic-looking. Indeed a few of my Sicilian relatives would not
look out of place at all in Tunisia or some other North
African/Middle Eastern country. My father has a Roman profile, with
straight black hair, light olive complexion, and hazel eyes. At
6'1" he's also rather tall for a full-blooded Sicilian so maybe
that's some Norman (i.e. ultimately Viking) ancestry coming
through.