Hydrangeas

It's hydrangea season in the Big Woods.  The bouquet on the table is real; the wreath hanging above it is artificial.  They look like they came from the same place; both have blue and white flowers.  The real white ones are oak leaf hydrangeas.  These grow very well in the Big Woods.

We actually have a bush of regular hydrangeas that is blue, and one about five feet away that is pink.  I always thought that the color of the blooms had something to do with the acid in the soil.  Does anyone know if this is true???