Raspberry plants prefer soil with a pH between 5.5 and 6.5. and when planted in alkaline soil they turn yellow. Raspberries do not like wet conditions and if the soil is very heavy this can also cause the leaves to yellow and then they are likely to wilt. If your raspberries are developing yellow leaves in the middle of summer, it's likely to be a deficiency in nutrients so it would be an excellent idea to top dress them with chicken manure, which is high in nitrogen, as soon as you can. However if its not Summer there and they are turning those colors they could have a virus. The only real way to know whats going on, is to send a soil sample to the soil lab and have it tested.