ive had a look in a wild flower book for you,but alass they only say sometimes they can be white of pink.
dosen't help really,but id like to knoe the answer as well,maybe it has something to do with the soil?
bulbaholic is probably the one who knows.

i cant spell either.

Are they reverting to type?

I suspect these are Spanish bluebells i.e. hyacinths planted in the garden rather than English bluebells (the Scottish bluebell is a campanula!) Either leave alone or remove.

I have white and pink native H non scripta from a bluebell wood. [given to me by the son of the owner ] They do that from time to time. Dont know why though.

The same in my garden. I have Spanish bluebells bought innocently over twenty five years ago, and a scattering of native non scripta, holding on, already in the garden, as it was once an old orchard. Both kinds come through pink and white. I too have no idea why pink might predominate over time. Most of my 2 kinds are blue.