Board Thread:Episode Discussions/@comment-1926479-20160705151842/@comment-26369387-20160705233111

^ Well, the thing is, with Hyūga, white eyes without pupils is their normal eye color, kinda like how Uchiha has black eyes for normal eye color, and with activated Byakugan, Hyūga gets veins and pupils.

With Himawari, however, she already has normal eye color, blue from Naruto, meaning that when she activates Byakugan, it would go straight from blue eyes to activated Byakugan with veins and pupils, as shown in omake. So OVA having Himawari activating Byakugan and veins not appearing at same time with pupils is a bit odd.