Could be so many things including seed source. You have a different soil, climate and time that the sun is up to the usual growing conditions of the Sugar Maple. The leaves do look like they might have fungal problems such as Anthracnose, but I would hesitate to diagnose anything this far out of my area.

Here is a link that might be useful: Fall colour in different locations.

Ciao, lucab.

Where do you live in Italy? I'm guessing the northern regions. Sycamore anthracnose, Gnomonia, has been found in northern Italy so that could very well be what the brown spotting is on your leaves.

It could also be caused by Phyllosticta or Septoria, which are common leaf fungi which occur in Italy. Those can be controlled to some degree with sprays.

As for the fall color, some sugar maples do turn yellow. As IpmMan wrote, it could be a genetic behavior, or it could have to do with soil quality. I have a Japanese Maple that turned scarlet red in sandy soil, and now in clay soil it turns maroon. (I also have a Persian Ironwood that should turn amazing shades of red, orange, yellow, purple, green etc., but it has only turned yellow.)

Perhaps you could plant a companion for your maple that has red fall color? If you can find one, you might try persian ironwood (Parrotia persica) and see if it will give you a red fall!

In Bocca al lupo!