This is Wet n Wild 1 Step Wonder Gel in Periwinkle Of An Eye (or "Peri-wink-le" if you must), 2 coats.
I said I was going to make "what color is this" a series (I've used it as a tag for some time), but this is already a(n) NOTD post and putting both would have made the title awfully long. But the way this falls under that tag is, is this actually periwinkle, or just blue? I just looked Periwinkle the color up on Wikipedia and the "official" version of periwinkle is pretty much pale purple. (It's actually exactly half and half cyan and magenta - 20,20,0,0, in CMYK terms -but I looked up purple and violet and both of them are officially more magenta than cyan. So I guess that means that periwinkle is a blue-leaning violet - officially speaking.) However, like many other plants (lavender and lilac come to mind) the colors of an actual periwinkle bloom can actually be all over the place. So - like many of my "what color is this" tagged posts - the answer is unclear. This polish is pretty much blue, with maybe a drop or two of purple - I thought I saw a slight purple tinge in bright sunlight, at least. I'd still call it blue, but I wouldn't be surprised to find out that there's a periwinkle cultivar that blooms in exactly this color.
Here's the swatch I posted the other day, for reference:
Aside: Looking for an internet rabbit hole to fall down? If you haven't read up about the color purple and the color violet and the differences thereof already, start here. Warning: veers off into science very quickly. But I was really fascinated, especially with the part about "Tyrian purple" and the reasons why only rich people could afford to wear purple. (Short answer: because more than 10,000 sea-snails had to die in order to dye a handkerchief!)