Experts and BHG readers answer.
Why did the colors of the iris's that I planted change?
Plants rarely change color; it's more likely that the blue variety you bought was more vigorous (which is the case with many of the blue and purple cultivars). The stronger and more vigorous cultivars took over your iris bed and elbowed out the other colors. Planting your iris farther apart will help keep any one cultivar from crowding out the others.