White-flowered plants

While walking at Ringstead Downs I came across these white-flowered plants of species which are normally shades of purple. I am not sure what causes this to happen but it is quite common in some species such as Common Stork's-bill and Marsh Thistle.

White-flowered Selfheal

White-flowered Large Thyme

Normal Small Scabious

White-flowered Small Scabious