Toxicity of UV inks is largely unknown as there has been little research in the area - but not all reputable artists refuse to not do any work in them - matter of fact, many of the best artists I know do some work in UV tattooing. UV ink does seem to have a higher frequency of reactions (like itching or minor skin irritations) than other inks used for tattooing - but many of the newer formulas are supposed to be much better. I've done a lot of research into UV inks, and honestly, the risks seem fairly minimal to me, to the point where I am considering getting one myself - and I'm not uneducated on matters of health and science seeing as these are my primary areas of study and research. Make the risk benefit analysis on this matter on your own.
White ink shows up poorly as much besides a highlight on most people's skin unless they have very little melanin (aka, they're pale) - most of the melanin in your skin is held in the layer above the tattoo ink - if it's darker than the ink, it hides some of the color... and I personally don't think an all white tattoo would look very good on someone who was fairly pale to begin with.
Tattooing in a color slightly darker than your skintone it a great way to have a subtle tattoo - especially when combined with either fine black outlining or an outline which matches the ink of the tattoo (this prevents bleeding since outlines are done slightly deeper and thicker... to my understanding of listening to an artist ramble at me and his apprentice). Find a good tattoo artist and discuss with them your needs and ideas for this tattoo, if they're halfway decent they will figure out a great way to give you exactly what you want!
I've worked in and out of tattoo shops for 3 years.