Remove the hydrangeas' leaves and place the stems with flowers in a vase with no water. Allow them to dry upright for two weeks.
Spray each hydrangea cluster. The best way is to remove a cluster from the vase and hold it by its stem. Then hold the spray paint can 10 to 12 inches away from the hydrangea blossom and spray it lightly. A few pumps on the center and sides of the blossom should be sufficient to maintain a dried but more colorful look. If you want more color, spray again, adding light layers until you receive the hue you want.
Affix the stem of each blossom to a clothesline with a clothespin. Allow the painted hydrangea to dry upside down for 24 hours.