Leaf yellowing and/or bleaching may be caused by Mosaic Virus or Herbicide Damage. It may also be an early indication of spider mite feeding.
Mosaic virus is a common cause of leaf yellowing and stunting in black raspberries, although it can affect blackberries and red raspberries, too. More raspberry virus information
Herbicide injury – Herbicides are also a cause of leaf yellowing in raspberries. Raspberries are sensitive to herbicides such as glyphosate (Roundup) …
… and Solicam.
Glyphosate injury may also result in more severe types of damage to leaves the following year, including strappy, stunted, narrow pale to pinkinsh colored leaves.
Princep may also cause leaf yellowing and/or bleaching though usually accompanied by leaf burning/browning.
Sinbar may also cause leaf yellowing and/or bleaching though usually accompanied by leaf burning/browning.
If leaves also have a yellowish orange powder on their undersides of leaves, this indicates late leaf (yellow) rust.