Why did some limelight flowers not turn white this year?

Hi Dolores! I saved this article from the Seattle Times... it helped me alot.

https://www.seattletimes.com/life/lifestyle/limelight-hydrangeas-offer-an-array-of-color-in-the-garden/

Hi Dolores. My name is Cindy. Your soil may be lacking some nutrients. That happens over time. I recommend that you mix one tablespoon of Epson Salt in a gallon of water. Pour it on the soil at the base of the plant. Then give it some more water. This extra will help the roots receive the Epson Salt quicker. This will put enzymes in your soil. Plants thrive with this. You can repeat every two weeks. Hope this helps. Good luck from Cindy.

There are fertilizers for the different colors of hydrangeas, perhaps one of them will help.