
Ambrato vermouth is an amber-colored aromatized fortified wine, sitting in weight between dry white and sweet red.
It is a dry style with a rich, honeyed body and a bitter edge, and most substitutes give you two of the three. Sugar is the easy correction; the bitterness comes back with a couple of dashes of a bitter, and the body does not come back at all.
Bianco vermouth
Sweeter, paler and less bitter, and it is the usual substitute; it needs help from a bitter to stand in for ambrato.
Dry vermouth
Paler, leaner and drier, without the honeyed body, and ambrato is a dry style, but a rich one; swapping in a bone-dry white thins the drink.
It is wine with spirit added, so it oxidizes like wine: fridge once opened, and use it inside a month. A bottle standing warm on a back bar is flat within a fortnight, and the honeyed note goes before the bitterness does.