It seems the fog is pretty heavy-handed in AC. A lot of the distant hills like at Mugello end up just looking like green silhouettes. You can edit C:\Program Files (x86)\Steam\steamapps\common\assettocorsa\system\cfg\weather1.ini to change this line:
BLEND=5
to
BLEND=1.2
This shows a little detail in the distant hills, and I reckon it looks better, on tracks like Mugello and Magione and so on.