They fade very quickly. Mine is essentially invisible now. I am very pale (I have to buy special foundation because all standard ones are too dark) and so my skin was the best kind to take white ink, but it still faded.
On taking the ink... Your skin type very much determines how it comes out. If you are very pale, it will come out like all the pictures you see on the internet. If you have a warm complexion or tan easily though, it will probably come out yellow. And god help you if you get it in the sun - some people report their white ink going brown and staying that way.
You will have to have the ink put in again about 3 times, which is expensive. If the ink is put in with a standard purple template, the template will contaminate the ink and make it a dirty grey colour.
Very few tattoo artists are willing to do it for the above reasons.
As stated above, white ink tattoos rarely last and for this reason, any reputable tattoo artist won't do one. The ink often disperses very fast, and after the initial tattoo and healing period, their 'suspended' effect fades to zilch and they just disappear. The ones you posted above are VERY fresh which is why they're so damn visible. There are NO healed photos of a white ink tattoo on the first 10 pages of Google images, and there's a lot of mislabelled scarification on there too.
Best bet is if you want something lasting that will give you your desired effect, find a modification shop that will perform electrocautery branding.