The latter. Marsica is a modern name, not necessarily what the area would have been called in antiquity.
We're used to seeing the tribal identifier as a plural on maps, but this is particularly difficult to work with. 'Marsia' just meant 'the land of the Marsi', thus I see no reason not to use that convention here.
Do you have any sources on this?
Yes :
the ancient Italic tribes come first of all from north and many before settling retained a certain degree of light features, the predominant ethnic type that made the upper classes of Rome .
For example there were even a whole tribe named "the blond ones" ( Rutulians) .
With the expansion Rome inglobated many other territories, and non Italic tribes as well with time , invasions and slavery the number of Roman citizens increased and slowly started to include people with darker hairs .
We have proves of many Romans having light features and a more nordic look :
R. Peterson’s fine study,
The Classical World (1985), which includes an analysis of 43 Greek, and 32 Roman figures, is persuasive. Dr. Peterson explains that the Romans painted their death masks to preserve the color, as well as the shape, of their ancestors’ faces. Blue eyes, fair hair, and light complexions are common. A good example of ethnic type is the famous portrait bust of Lucius Junius Brutus, the founder of the Roman Republic, which dates from the fourth century BC. Brutus’ face is identifiably northern, and so is the color of his eyes.
The sculptor used ivory for the whites and blue glass for the pupils.
Another classic example is the famous fresco from the Villa of the Mysteries in Pompeii, which shows four women undergoing ritual flagellation. They are tall, light-skinned, and brown-haired.There is also evidence from Roman names.
Rutilus means “red, gold, auburn” and stems from the verb
rutilo, which means “to shine with a reddish gleam.”
Rufus, meaning red, was a common Roman
cognomen or nickname used for a personal characteristic, such as red hair.
The Flavians were an aristocratic clan whose family name was derived from
flavus, meaning golden-yellow. The Flaminians were another noble family whose clan name came from
flamma, meaning flame, suggesting red hair.
According to Plutarch:
Marcus Porcius Cato had “red hair and grey eyes,”
Lucius Cornelius Sulla, the general and dictator, had “blue-grey eyes and blond hair,”
Gaius Octavius (Augustus), the first Roman emperor, had “bright eyes and yellow hair.”
And so on with others as well.
Recent analysis of an ancient marble bust of the emperor Caligula found particles of the original pigment trapped in the stone. Experts have restored the colors to show that the demented ruler had ruddy skin and red hair.
Romans were a Latin people and were one of eight Italic tribes — Apulii, Bruttii, Lucanians, Sabines, Samnites, Umbrians/Oscians and the Veneti — who migrated into the Italian peninsula around 1000 BC they split from a proto Italoceltic tribe before coming into the peninsula.
Of course, Italy was not vacant. The Etruscans lived to the north of Rome in what is now Tuscany, and there were other darker-complexioned whites living in the peninsula. The Etruscans are likely to have been Carians from Asia Minor.
A short list of emperors :
Of the 18 Emperors from Augustus to Commodus: 9 had blond or red hair; 5 had grey or white hair; 3 had no recorded hair colour, and just 1 (Hadrian), was referred to as dark-haired.
Of the 18 Emperors from Augustus to Commodus: 9 had blue or grey eyes; 2 had "wine-coloured eyes" (whatever that may mean), and 7 had no recorded eye colour.
To resume, Italic Tribes had a quite consistant number of blonds and light eyed people, Local Italian tribes before Italics had light skin and darker hairs, Greeks had less blonds but still had a few.
But I am not saying that the majority of Romans were blonds, just that they had a few and in higher numbers than modern Italy proportions.