Persona 4 The Golden's bonus PlayStation Vita skin was announced a few weeks back. Metal Gear Solid HD Edition's skin was announced earlier today.
It turns out that these skins are part of a Sony campaign. Persona 4 The Golden, Metal Gear Solid HD Edition and Gundam Seed Battle Destiny, all June releases, will include a free skin and a matching wallpaper. The skin protects your system's screen and body and also makes it looks like you own a specially crafted Vita.
Visit Sony's campaign page here.