Can you buy alkaline at the garden shops? I wasn't sure how to keep them pink.

I'm not sure that you need to. Here's a couple pictures of my Hydrangeas -- right next to each other -- and I feed them nothing!






And a couple feet away is this young one:



I think the newer varieties don't require the soil amending that the older varieties did.

Great to hear! Thank you.

In a large hydrangea bush with a large root structure the distribution of ph in the soil is going to be a little varied. Where the ph is higher, the blooms will be pinker, and will be blue where the ph is lower. If I remember correctly the element is aluminum that creates the variance in color. The higher the aluminum sulphate the pinker the bloom will be, and the opposite if blue. So that's why on a single plant there can be more than one color, including a purply tint; it all depends on the soil content where that branch's root is feeding from. Of course you can control it better if you keep the bush potted, but that could limit the size. Is that all clear as mud?? Hard to explain, you almost have to visualize it, I guess.

On the other hand, I could be totally wrong, but it seems that way to me.

If you have a bush with white blooms, they'll remain white throughout their life, but will sometimes get a pink tinge as the blooms age.

Aluminum sulphate will make your soil acidic, lime will make it alkaline. Susan, your soil is naturally acidic in this area, especially if you have a lot of pine litter like I do. You could have it tested to find out exactly how much lime to add, or just start with a light amendment and add a bit more at a time until you start getting pink blooms - too alkaline can kill plants, just like too acidic can, so it's best to start slowly.

(I don't know a thing about hydrangeas, but I'm pretty decent at chemistry )