Hydrangea Happiness

Hydrangeas have always been close to my heart. I know have three of them in my balcony garden. They are in very big pots and each of them is unique in its colouring. This is my latest addition, a gift from my son for Mother's Day and my birthday combined (only a day apart in May!)
I'm going to try and keep this one in blue and lilac tones with a hint of pink. I have a special fertilizer that is supposed to do that! 
If anyone has any tips for keeping hydrangeas blue, I would love to hear them!