Now that you have completed cutting back your new wood blooming hydrangeas, it's time to look at what's happening with your old wood plants. Which ones are these? Your old wood plants include hydrangea macrophylla (big leaf), hydrangea serrata (mountain), hydrangea quercifolia (oak leaf) and hydrangea petiolaris (climbing) . Even if your plant is a rebloomer it retains old wood flower power and buds can be there that formed on last year's growth. 

In my April Connecticut garden, the first hydrangeas I'm pruning are the ones that flower on the growth they will put on this year, better known as "new wood." In hydrangea-land, those are hydrangeas arborescens or woodland/smooth hydrangeas like 'Annabelle', or for example any plant that has Incrediball® or Invincibelle® in its name. There are many others. They will all have "arborescens" as the second part of their name. The flowers are round and either white or shades of pink. None are blue and you can't change their color.