Achillea millefolium featuring pink buds instead of white

Disclosure: I am not a botanist, just a hobbyist who dabbles with growing things. (You've likely figured this by how I'm posting anyway.)

I purchased at my local farmers' market (Northern Coast of California) some Achillea millefolium advertised as having a white bloom. It has begun blooming and, imagine my surprise when it was pink! Is this a separate variety or just some manifestation of Mendellian genetics? Or were there some deleterious influences (overcrowding, perhaps, or uneven watering) that caused the mutation? (I realize I've slacked off a bit lately in my watering duties. I'd gotten complacent with the rains coming.)

TIA!