There are purple, dark green, and blue-green types. There are small early kinds for quick single crops and large plants that bear for months. There are even overwintering broccoli that bear purple sprouts very early in spring. We recommend planting a few kinds for longest harvest and mealtime variety. Very high in antioxidants.
These have two possible life cycles--annual and overwintering. The annual types are planted and used the same season, usually making a very fast crop one time. The overwintering kind makes a huge plant that is planted in fall, goes through the winter, and then makes hundreds of heads over a long period in early spring. You will probably want both, since they have different time slots and uses.
Brief overnight frosts are fine; broccoli is very hardy. Protect the heads from too much rain, which will cause rot and mold; row covers or a cold frame work well for winter crops or getting an early start.