One of my favorites have always been hydrangeas but unfortunately due to my poor soil and bright sun, I can't seem to get them to grow. My grandmother on the other hand, had huge hydrangeas growing in her yard, she had a nice shaded yard full of plants but the hydrangeas are the one thing that I always adored and remember the most.
Back then they didn't have all the hybrids so the standard plant that was either white, blue/purple, and pink is what you got. The actual color depended on the soil acidity and whether or not you did what grandma did... add Kool-Aid packets to the soil.
Adding lime and other nutrients to the soil to adjust the pH is the simple trick to turning hydrangeas the color you want. My grandmother would add the Kool-Aid packets and water them in. When the plant absorbed the water it was also absorbing the powdered dye from the Kool-Aid... turning them a variety of colors, and rarely two blooms would ever be the same.
How to Change the Color of Hydrangeas
To obtain a pink Hydrangea blossom maintain a soil pH at or near 6.5 For blue or purplish colored blossom, maintain a pH at or near 5.0. If you want to change the color of your hydrangea then you will need to alter the soil accordingly.
How to Grow Hydrangeas has lots of information on how to properly grow, care for and change the color of hydrangeas. The pictures are beautiful and includes the new varieties that have the multi-colored blossoms. If you would like to know more about propagating hydrangeas, changing the color or anything else hydrangea-related you can find it all at: How to Grow Hydrangeas