They differ in ways other than fruit color. Red raspberries have erect canes and are propagated by suckers. These are usually grown in the Western States. Black raspberries have arched canes that root at the tips.
Purple raspberries are hybrids of red and black varieties.
The black and purple varieties are grown in the Eastern States. Varieties of blackberries include boysenberries, ollalieberries, loganberries and youngberries. Boysenberries are reddish black with an aroma and flavor similar to raspberries. Ollalieberries are slightly longer and more slender than the boysenberry and are a cross between black, logan and youngberries. Raspberries grow best in cool climates.