Your brew should turn out tasting fine. Wort will darken during the boil if high heat is used for long period of time (caramelization usually from direct heat on a stove top or when directly on a gas flame), partial boil, high gravity wort and especially when using extract.
A vigorous boil does a lot more than just pasteurize, the boil helps with hop utilization and large protein formation. If your worried about color I know a few who did a 15-20 min boil and adjusted their hop additions accordingly and ended up with a good beer in the end.