As far as I know there is no White Knock Out. There is a rose by Radler called White Out but it is not a part of the Knock Out series and I don't believe it is related genetically.

There is a new Radler climber called 'Cloud 10' (Radclean) that is supposed to be very disease resistant.

Here is a link that might be useful: Cloud 10 @ helpmefind

Most of the Knockouts are not "genetically related" to each other. It was a vast selection process that tested for blackspot resistance that got to those particular half dozen plants that are sold under the branding of the Knockout series. The cleanest one in each color group was the one that made it.

While not white, the one nursery rose that stuck in my mind last year was Radlers " Peppermint Pop"

When we moved in two years ago, the previous owner told me the 5 white roses banking the porch were "white knockouts." I didn't know anything about them. I tried to research, and the white out roses appear single. The roses near the porch are very double. All I can think is that they are Icebergs and maybe someone told the previous owner that they were KO's meaning that they were the white answer to KO's because of their bloom reliability. I can't think what else could have happened. Of course, I am out there spraying fungicide every two weeks, because they are blackspot magnets - that's what makes me think they are Iceberg. ;)

Same mystery around here. Neighbor put in a berm along the road and planted a shrub border, with a variety of shrubs (good ole green shrubs) with a white shrub roses interspersed. They are perfectly healthy and bloom consistently. I asked and he told me they were White Knockouts.. and the beat goes on...
Guess I should look at hmf for White Out and compare it to his.

Maybe this is where the confusion originates (taken from Edmund's Roses listing for the rose "White Out":)

" Very compact and disease resistant, it's the closest thing to a white Knock Out and a much better alternative than the usual Iceberg or Seafoam roses. While not completely immune to black spot, the problem is never extreme to the point of it being detrimental to the plant or landscape. Until a black spot-free white Knock Out is hybridized, this is the best alternative. "

People do tend to have selective memories. They remember the name Knock Out and that's what they repeat.

I think you nailed it, Anne. :)

Hello Emily
Please let me know would you like to trade drift rose cuttings. I have gold medal,queen Elizabeth,and double delight,st Patrick rose .i can trade cuttings.
Thank you

Bottom line is there is no white knockout.
Only white out rose bred by same guy (Radler).

My mom has sunny knockout. It starts out yellow and fades
quickly to a off white color.

Article below explains:

Here is a link that might be useful: White KnockOut Rose?