When I cut in a yellow beet I found the rings discolored like in the photograph. Not white like the other beets. Safe to use or not?

It's just a variation, which does happen sometimes. All beets are related to one another, and sometimes you get a throwback genetic variant. Kind of like how brown eyed parents can sometimes have a blue eyed child. You can get discoloration in sliced yellow/golden beets after peeling and cutting due to oxidation, and they will turn black in time. But the beets in your picture look pretty much like the ones I just canned for winter eating. So I'd think yours would be quite safe to eat.

That’s the way my yellow beets look.