Vexillology

Wikipedia article about the flags of Napoleonic Italy

The Napoleonic Republic of Italy encompassed only a small part of northern Italy, as shown on this map:

Nonetheless, the flag lives on today in the presidential standard of Italy:

The colors are of course unequivocally Italian. However, the choice of colors to represent Italy, first occurred with the Napoleonic invasion. Before that, there was no unifying Italian symbol, as Italy was fragmented in state. The exact origin of the color choice is unclear.

The lozenge (the diamond) is a peculiar feature of the flag. It occurs rarely, the most prominent example of course being the flag of Brazil. A similar flag was used by the Second Republic of Venezuela 1813-1814.

The lozenge seems to be a feature of French military flags, that came in vogue at the time. See this discussion on the question: https://history.stackexchange.com/questions/35824/how-can-a-diamond-shape-be-a-reference-to-napoleon