Last week in Rome three mannequins doused in fake blood were discovered in front of a municipal building ahead of a visit from Italy's first black minister, Cécile Kyenge. Flyers scattered around the area declared: "Immigration is the genocide of peoples. Kyenge resign!" This is only the latest in a succession of shocking attacks and threats since Kyenge took office in April. She's been compared to an orangutan by a former government minister; likened to a prostitute by a deputy mayor; and had bananas thrown at her while making a speech.

Her appointment has not only shed light on the country's problems with racial tolerance, it has begun to strip away at the Italian stereotype: Italians are friendly and kind, love to laugh, and enjoy the good life. They are, after all, more Mediterranean than European, a bit disorganised, but more likely to welcome you with open arms than insult or threaten you. It is a concept that goes by the term Italiani brava gente: "Italians are decent people". It was this idea that drew me to Italy as the subject for my new book. It ran counter to the experiences of my grandfather and his generation, who fought against the Fascist invasion of Ethiopia and endured a five-year Italian occupation. That contradiction took me to Rome, where I lived for an extended time, and where I researched Italy's colonial-era archives.

The Fascist leader, Benito Mussolini, and his party ruled from 1922–1943, during which time Italy moved to expand its empire beyond Libya, Eritrea and Somalia. In 1935, Italy invaded Ethiopia. Its people faced a devastating combination of aerial warfare and ground assault. They were subjected to mustard gas, concentration camps, and massacres. These were tactics Italy had developed in Libya in what would be a brutal 30-year struggle, one that Italy euphemistically labelled a "pacification campaign".

Italy routinely censored accounts of the war in Ethiopia; reports stressed instead Italy's civilising mission. Language was carefully crafted to bolster Italians' confidence not only in their right to take another people's land, but in the benevolence in that act. Italy emphasised the construction of infrastructure without revealing that these roads, bridges and telephone lines were built to improve mobility and communication between military forces and came at the expense of human lives.

While Italy's efforts to shroud the bloody side of imperial ambition don't make it any different from other colonising countries, most striking is the near-absence of this history from textbooks and national dialogue. It was not until 1996 – 60 years after the fact – that the Italian ministry of defence admitted its use of mustard gas.

If Germany had its Nuremberg trials and South Africa its Truth and Reconciliation Commission, then what is missing in Italy is the kind of postwar accountability that forces harsh truths to light and begins the difficult journey towards reconciliation. What these moments of acknowledgement have shown us is this: addressing painful facts cements collective memory, establishes a collective ethos, and helps develop a vocabulary for repentance. It brings together those who once held the power to hurt and those who have the power to forgive.

It is through language that a nation transforms itself, and creates national identity. Italy's task since unification in 1861 has been to forge a unifying set of traits from strikingly different and often contentious groups of people. There is a popular quote attributed to the statesman Massimo d'Azeglio that says: "We've made Italy. Now we have to make Italians." Any kind of collective character has come from deliberate and careful construction. It is one that has historically included white skin. It is this that's challenged by Kyenge's presence.

Italy, whether it wants to or not, is undergoing transformation. First- and second-generation and native Italians are creating some of that momentum: striving to change discriminatory laws; and fighting for greater awareness not only of Italy's past, but its future potential. There is hope, but there is far to go.

I am reminded of a dinner in Rome with friends and colleagues. The celebratory night was soured by a comment shouted out that involved my skin colour and food and a vulgar sexual innuendo. The friends beside me were aghast. When I looked around, an elderly man winked at me. I started to protest and he threw up his hands and laughed. Then he went back to his conversation, and pretended I didn't exist.

If one hadn't heard what he'd just said, he would have looked like a good-humoured man misunderstood, unduly put upon. He would have been the typical easygoing Italian, another member of la brava gente. The attacks on Kyenge have been much more virulent; it has been hard to see the jovial Italian behind the vehemence. But the myth persists in the absence of harsher sanctions against those politicians and groups who are responsible. A national reckoning must involve all Italians.

On hearing of the latest abuse directed at Kyenge, I contacted an Italian friend of Somali descent and asked what she thought. "This is my country," she said. "We're working to improve it. Now more than ever, Italy needs people like me."