Their eggs are not always brown. They can be light tan (usually when the hen is young) or they can be medium tan or darker tan. I wouldnt classify their eggs as really brown, at least, not compared to (hatchery stock) Marans or Barred Rocks. I have pure, non-hatchery stock Jersey Giants from very reputable breeders, and none of them lay a 'brown' egg, all are in the tan family. Maybe because the hens are less than 2 years old? I know their eggs are huge, but not anywhere near the color of my Marans or Barred Rocks. All mine lay tan eggs.
There is a thread purely dedicated to Jerseys- I think it has some egg pics, and alot of great info.