As someone with a tattoo that has a lot of white in it, I'd be cautious about having an all white tattoo!
Unless you have a very light skin tone and are able to just use white as a highlight as opposed to packing it in the entire area, I'd advise against doing an all white piece, especially with no hard/dark lines, as the longevity of the tattoo will diminish significantly. White ink is the fastest colour to fade, and then not having distinct black line work can often cause tattoos to become blurry quite rapidly.
I'll also mention white ink tends to "oxidize", as it's usually titanium dioxide based, so for some people that can make the white turn a creamy yellow/tan colour over time. Just some things to consider if you haven't already!