It's the sandblasted finish which was about £50 more than the standard brushed finish if I remember correctly.
Tires - it'll take up to 2.4in, on singlespeeds I generally prefer to run a slightly narrower tire at higher pressure so 2.4 would be the absolute max I'd ever want to run on this.
I've since had them build me an all-road bike as well - equally as pleased with this so I'm a bit of a titan fan-boy now!