These flowers are Hydrangeas. The pink color of most of the flowers is an indication that they are not getting much aluminum, which they need to produce the blue pigment. This either means that the soil is poor in aluminum, or that the pH is high (alkaline). A low pH (acidic) makes it harder for the plant to absorb aluminum. Without the blue pigment, the flowers are pink. The more aluminum the flowers get, the darker blue they will be, so adding aluminum sulfate to the soil will make them bluer. Since the roots spread over a large area, some may be delivering aluminum, while others do not. This can result in different colored flowers on the same plant, depending on which roots are supplying nutrients to each flower.