I've seen this type of mani stamped many times. I really like it, but being that I don't stamp, I freehanded it and I just have to deal with imperfect lines.
I used three new polishes for this mani. The hubs and our daughter picked these up for me for my birthday a couple months ago and this is the first time I'm using them. Portobello, Holland Park and Notting Hill Gate are three new neon shades from Nails Inc. These are all jelly-ish; not in your face jellies, but not full on cremes either.
Because these polishes blended so well together, to do this gradient I just polished them each on one after the other. No sponges necessary. I used a small striping brush and black acrylic to do the stripes.