What variety of hydrangea are they? Not all will turn pink :-) And the amount of shade can have an impact on how the flowers color as they age

I am pretty sure they are the Nikki blue and they get a couple hours filtered sunlight.

Nikko-- excuse the typo
The blooms were pink last year

You probably got pink last year because that was what the minerals and pH in your potting mix made the blooms do. But now that the roots are absorbing minerals from your garden soil in larger amounts, the blooms change color based on soil pH and the amt of aluminum in your garden soil.

NB blooms can turn somewhat clear/light blue when the soil pH is close to neutral. If your soil has plenty of aluminum and the soil pH is acidic, the blooms will turn shades of blue (the more acidic, the darker the shade of blue).

Thank you for the responses. Could you recommend what I should added to the soil to make the soil better for them?

Plain ole mulch and organic compost in Spring will be great for them. Say, a layer 1/4 to 1/2" of compost around each shrub. You can also use 1/2 cup to 1 cup of cottonseed meal. A balanced slow-release fert like Osmocote 10-10-10 will also be fine. You can add 3-4" of mulch up to the drip line too (a little further if it is windy).

To turn the flowers pink, you need to regularly amend with garden lime available at nurseries. Apply according to the label's directions and then water them. To turn them blue, add aluminum sulphate instead (or try greensand, iron sulfate or garden sulphur). Apply these according to label directions and then water them. Do not exceed dosages by a lot as sulphur based compounds can burn the small roots. See if you can also invest in a soil pH kit so you can measure the changes in soil pH. These are commonly available at plant nurseries but I am not sure how the stock will be near the end of the growing season. If everyone around you is out, wait until Spring or mail order from someone you like.

Fertilizers should be applied thru the end of June so the plant will go dormant in the Fall and not stay in growth mode. This does not apply to the lime and acidifying soil amendments. You can also use some "weak" fertilizers like liquid seaweed, liquid fish or coffee grounds but again, stop using them in July-ish.