(image via flickr user roman.noven)
Because Aurora are produced by gases emitting photons at specific wavelengths, they can't be white - most of the time they are the green and red emitted by oxygen, as in this photo I took in Guelph, Ontario:
If they do appear white, it's likely a different phenomenon, or them being too faint for the eye to determine the color, or an effect caused by the colors blending together. White light is a mixture of colors that can separated into a spectrum or rainbow by means of a prism.
The first photo a long exposure of people waving florescent tubes under electric lines - this causes the tubes to brighten. One very obvious thing about the first photo is that the light is below the electricity lines, which they block out in some places - if they were aurora, they would be blocked out by the lines, like the aurora are by the trees in my photo.
roman.noven did a series of these photos in 2010, including the one that's been circulating as the White Northern Lights in Finland, which can be seen here: https://www.flickr.com/photos/10332728@N06/sets/72157624374696833/with/4795525179/
Note that in one photo, a group of eight people holding tubes can be seen posing under the power lines.
roman.noven 's flickr bio describes them as Roman Noven and Tania Shcheglova, from Ukraine. They are well established professional photographers with a website here: https://www.synchrodogs.com/