Hard to see from the image, but some of the white flowered ones have petals the same colour as the sepals.

is it a young plant? it may not have settled enough to make full flowers. Stop feeding it for a while as whilst it is being fed then foliage will take precedence.

Thanks Owdboggy, but there are no flowers inside the outer cups even though it still looks pretty.
Thanks Seaburn, I only bought it in the spring so will leave it to it's own devices for now.