What’s going on?

Can anyone tell me what’s going on with this hydrangea?
I have lots of hydrangeas in pot all together. Waiting to go in the cottage garden as a hedge.
I notice a couple of days ago a small head of lovely blue very small spiky (star like) flowers. Wish I’d photographed it then. Because this morning I noticed that lovely blue completely different shaped flowers was actually part of a plant with the usual big head rounded petals and pink!

         

Definitely the same plant. I checked it wasn’t too in the same pot. 
Any ideas?

I always believed the soil acidity dictated hydrangea colour? Blue on acid soils and pink on alkaline soils?

I don't understand the question! Is it the shape of the flowers or the colour?

I don't understand the question! Is it the shape of the flowers or the colour?

Both . Different shapes and colours on same plant.

Do you remember where the cuttings came from? Maybe it was a special variety? My bog standard ones change colour all the time - there's pink and blue on the same bushes. I'm not sure what they're supposed to be - they've been there for years.

There’s a couple of locations it could have come from. One of them does have some very interesting varieties.

I suppose if the soil was neutral,neither acid or alkali you could get differing colours on same plant?