You are probably referring to the change in color that many hydrangea blooms have, starting at the end of summer (more or less). If so, the answer is no. Hydrangea blooms naturally go through a color change that varies dependng on the variety. Some start white then they turn a shade of pink and finally turn brown. I have some that start pink, turn dirty white, then green and then brown. You can deadhead them if you do not like them or enjoy the plethora of color changes that they grow through.

For information on deadheading, click on the link below and scroll down to the paragraph titled Removing Old Blooms.

Here is a link that might be useful: Deadheading and Pruning Info

In other words, the "greening" is a normal process of aging.

Next year, the fresh blooms will again be white.

My white hydrangeas also turned green, but are not old. Initially the new flowers started off white and then turned green. Thereafter new flowers started off green and stayed green. It is only the beginning of summer in South Africa.

My suspicion is that in early summer they receive a lot more sunshine. As the summer progresses it becomes more shady, thus the flowers turn green.

I plan to move them to full sun and then see if that makes any difference. Should have the answer next year this time.

"I plan to move them to full sun"

zs6awo, do you know what kind of hydrangeas you have? There are some kinds that are fine in sun in some areas (Hydrangea paniculata in my area, 43 degrees north), but many types won't be happy in full sun (H. serrata, H. macrophylla, H. arborescens, H. quercifolia). IME amount of sun doesn't influence the flower color except that in sun-stressed plants the color fades to green or brown faster.

You are much closer to the equator than I am, so I doubt moving your hydrangeas to full sun will please you.

Well, down here, the amount of sunlight can affect the flower color. Hydrangeas like Annabelle and Little Lime tend to stay green all season when planted in locations with all-the-time indirect sunlight (or they turn white very late, as in September or October). The amt of blooms is not affected. One surprise... I actually liked the look of lime green Annabelle blooms more.

I would be careful to move Annabelle-type of hydrangeas to full sun as they do require more afternoon shade. Paniculatas here do best in sunny locations but still require afternoon shade or the leaves will burn. But in the northern states, paniculatas do fine in full sun.

Mophead Mme. Emile Moulliere here handles a bit of extra summer sun fine but I have to give it a lot of water (in addition to the regular amt from the sprinkler system). Any white reblooming mophead bloom that has changed color could be pruned to see if triggers another bloom (more difficult to do the further one progresses in the Fall months) but it would be interesting to try in really southern US locations like FL where the plants go dormant in January ish.

So, instead of transplanting them, consider putting them in a pot and move the pot around as needed until you find the perfect location. Once you find a good spot, plant it.

Thanks, Luis. I don't have any in full shade, but I don't think I've ever seen hydrangeas around here with only green flowers. I don't know if that is because no one plants them in full shade or because our sun angles are such that it's difficult to find spots with no sun in summer at this latitude - the sun swings rather far north both morning and evening.

orange for Halloween. red for Valentine's Day and so forth!

I HIGHLY AGREE with the "tub test" method to see if a hydrangea likes a spot. Use a larger tub size and you can take a year or two to decide by seeing plant response.

Everything you see below was part of a staging test for our backyard in tubs. It was too hot to plant safely until fall so we did a sun/light test for the plants. It also helps you envision final effect better.

Once the light location is right, you can add more or less amendments to get moisture and set bed cultivation depth right. I also install plastic liners or basins underneath beds where I need boggy effects or more water supply.