Purpling of leaves is frequently a sign of stress, cultural, weather or mineral. Adding aluminum sulfate can shift the availability of Phosphorus to the plant, causing color problems. Most hydrangeas prefer a slightly acid pH, but a soil test will tell if the pH has been shifted too far. 5.2 pH is good for the blue tones usually. There are different cultivars and each has its own needs.

P is usually rather slow-acting. I am not familiar with liquid bonemeal, , but fish emulsion, is a quick feed and usually not unwise, but be aware that boosting P too much is a problem for the environment and the plant. Have you done a soil test analysis?