French Hydrangeas - how to make a color change

For blue hydrangeas - soil should be acidic (pH of 5.5 or lower).  This allows for the plant to utilize the aluminum in the soil producing a blue color. 

To get blue, you can acidify the soil by dissolving 1 tablespoon of aluminum sulfate per 1 gallon of water.  Drench the root zone in April/May time frame.

To get pink, you can dissolve 1 tablespoon of hydrated lime per 1 gallon of water.  Drench the root zone in April/May.

If you want white, certain types of hydrangeas will stay white regardless of pH.  Example is Madame Emilie Mouillere.