Blueberry leaves are getting red and have little red spots
There could be a lot of causes for reddening of the leaves. lack of nitrogen, lack of phosphorus, cold weather, wrong soil pH.
If it is just the new leaves and they look better as the mature I think it is just a response of the young leaves to intense sunlight when they are young and as the leaf matures the protective red color goes away. If you have any information about a specific pattern to the reddening let me know.
I often see small red spots on young leaves and have never been able to determine that they were due to any disease or other cause. They cause concern when growers see them but they seem to go away without leaving an permanent marks. Have you sprayed the plants with anything that might have caused a reaction in the young leaves?