These color changes processes are not things that happen quickly as they entail ammending the soil with slow acting materials forever. Your soil in Georgia is naturally acidic, with pH readings below 7.0. A reading of 7 means your soil is neutral; a reading below 7 (such as 6.5, 5, 4.5, etc) indicates an acidic soil whereas a reading above 7 indicates that the soil is alkaline.
To make your soil more alkaline, add some garden lime under the shrub's canopy according to the package's directions. If you have a pH meter sold at some nurseries, you can begin testing before adding the lime and then test again every few weeks or once a month. The soil in your garden has a propensity for reverting back to its original state so these amendments have to be done forever or the soil will "automatically" revert back to an acidic pH. The change back will not happen quickly either so do not panic if you forget to amend on one month. You have to give time to these changes. While you are at it, ament the soil with extra phosphorus as this also helps produce pink blooms. That is because phosphorus, in large enough quantities inhibits the absorption of aluminum and that mineral is needed to get blue blooms in hydrangeas.
Because of the soil's buffering capacity, some times it would be best that you do this by growing the plant in a pot instead of the ground. In a pot, this process is easier to control and maintain.
Because the process is so slow, I would start n o w. The more acidic your soil is, the more time it will require to change into something that is neutral or alkaline. For that reason, it is a good idea to invest in a soil pH measuring kit.
Buying a soil pH kit from nurseries is a good way to track how the soil is changing. While cheapo kits are inexpensive and not that accurate, they give you a general idea of how the soil is changing by displaying colors when you mix a soil sample with water. You can also buy fancy ones that approximate soil pH scale measurements instead of giving you colors. If you use those, note that a change from 5 to 6 in the pH Scale means that your soil is 10 times more alkaline than it used to be (the scale is logarithmic)