Leather was an option for the Stilo, albeit quite rare.
Most leather interiors are black, although rarer still is the 2 tone ivory and black leather. If you can find a set the swap is really quite straight forward, even if a bit time consuming. Be sure to get the door cards and centre arm rest cover too.
I've read of people swapping the front seats from an Alfa 147 in to a Stilo, which apparently is do-able with very minor modification to the runners. Rear seats will not fit though as the split is wrong (60/40 vs 40/60). A good retrimmer would be able to get it sorted on to the stilo frames though.
3 door and 5 door interiors are obviously different, so if you've got a 3 door, buy a 3 door interior and so on.
