Symptoms typical of severe anthracnose infection on blackberry.
Whitening of drupelets on the fruit, mainly on the upper surface of the fruit and on the side of the row which receives the most sun, is as you can guess, due to sun exposure. This problem is also frequently seen on red raspberries and may occur on both crops at the same time. It can occur whether temperatures are high or not and is often more noticeable following a period of very clear days. There is no cure, and the problem clears up once weather conditions change.
Drupelet reddening, often only apparent after the fruit has been refrigerated, is thought to be related to the fruit basically getting "cooked" when it is on the plant close to harvest time. Apache seems to be especially prone to showing this symptom.
With both of the above physiological problems, drupelets remain full-sized and plump.
Insect feeding, such as from stinkbugs, damages drupelets and may cause their color to lighten. The damaged drupelets occur in a random pattern on the fruit, depending on where the insect stopped to feed, and often eventually collapse.
Anthracnose causes fruit to turn brown and possibly seedy in severe cases, and some or all drupelets on a berry may be affected. If you suspect anthracnose on the fruit, also check the canes for anthracnose lesions and the leaves for spots - if you find numerous lesions, this is a clue that the fruit problem is caused by anthracnose. In severe cases, the cane lesions can cause cane death. If anthracnose lesions are present, fruiting canes should be pruned to the ground right after harvest, pruning stubs should be removed during dormant pruning, and fungicides (see the Mid-Atlantic Berry Guide for materials and timing) applied.
Other issues that affect water translocation can also cause fruit to dry up, including winter injury, mechanical damage, and other cane diseases such as Gnomonia stem canker which may essentially girdle the canes. If the fruit is drying up, the problem may actually be much lower on the plant.
Finally, spotted wing drosophila egg-laying can damage drupelets and cause them to quickly collapse. Spotted wing drosophila numbers are on the rise, and blackberries are among their favorite foods, so be on the lookout.