Eleven subspecies of the White Wagtail (Motacilla alba) are currently recognised and they all have slightly different plumages.
This is Motacilla alba alba, the nominate subspecies of the White Wagtail which occurs on the European continent and migrates down as far as Kenya.
M. a. alba winters in the south part of its range and West and East Africa, Arabia and South-west Asia.
Another subspecies, M. a. dukhunensis, may occur in Oman in winter but the upperparts of this subspecies are paler and more blue-grey than M. a. alba, and it has wider whiter wingbars and tertial edges.

1st & 2nd photo: Mudday, Dhofar Region, Oman, 8 February 2017
3rd photo: Ayn Razat, Dhofar Region, Oman, 6 February 2017
4th photo: Raysut Wast Disposal Site, Dhofar Region, Oman, 5 February 2017