Fiat make cars, and paint them. One colour they use is called Giallo Ginestra, Once translated, this Fiat colour becomes Fiat Broom Yellow. Why broom..? Ginestra is a common enough plant in Europe; it's UK name is 'broom', and it's a strikingly bold yellow. This is a photo of ginestra, or broom...
There; that's the origin of Fiat Broom Yellow.