Sue, I have been intrigued by these white tattoos! Spoke with my tattoo guy (yeah, like I'm covered head to toe with tats, NOT!) He said that the look of white tattoos is determined very much by your natural skin pigment. If you are one of those Caucasian people with blue/white skins, the white looks bright. The more Latin or Asian your ancestral influence, thus perhaps more sallow or olive toned skin, this makes the tattoo look more yellow than white.
He also said white is very prone to fading and should mostly be used in a place that is not exposed to the sun. He claims that on arms, for example, they are not a long lasting tattoo.
At my advanced age, how long a tattoo lasts is not a concern.