Remember seeing on here someone has a Willy3 without a sunroof, but apparently its one of a kind!
The 3 is a different blue from 1+2, Monaco Blue and Sports Blue respectively.
From comparing my 2 to a friends 3, we noticed the dash is lit differently on the Williams3. The warning lights are more "hi-tech" looking on his, whereas mine are more obviously just bulbs behind the plastic!
If you do a search for "Williams", or "Will" (so you catch "willy" threads too), youll find the definitive list, as the differences have been talked about loads before