Why is it that some Daisies are pink, when they are mostly white ?

I don't know about your particular plant, but I have seen some plants change flower colour after a visit from their preferred pollinator(s).

The name "daisy" is pretty much generic for a certain flower form. There are hundreds, if not thousands, of different types of daisy, and they come in all sorts of colors. I have in my gardens daisies that are white, yellow, bright red, and three different shades of blue.

Looks like a Fleabane by it's common name, an Erigeron, that's normal, depends on age of bloom.