Two things to follow up on:
1. HERE I talked about getting your hydrangea to bloom, by using coffee grounds. I'm happy to report that 2 out of 3 of them are bursting with glorious blooms. It really does work! The problem with the one, was it only put out 2 blooms, but, its also a species I'm not fond of (Lacecap) so I'm not crying over it.
2. Changing the PH of your soil, in most cases, can change your hydrangea color. ( like I said before though, white hydrangeas usually do not change color, and consider yourself lucky if you have a white mophead hydrangea )
2 years ago I dumped wood ash over 2 of my hydrangeas. They were the classic blue that is very common, but I was looking to see if I could get a change out of them. So THAT next spring, it changed to purple and then burgundy in the fall. I was in love. Then THIS year, they are PINK. I am completely thrown. I plan on trying to neutralize the soil this winter to get back to purple, OR I'll dump MORE ash on it, to see if it'll give me dark dark pink. Reguardless, it's a fun experiment.
Here are a few unedited pics I took today of all the different colors and species I have in my yard today.
( This first one was bright blue 2 years ago )
One of my Lacecaps: