Though the PS Vita currently does not support Themes, some designers have gone and figuired out a way to basically install a theme for your PS Vita, images inside......
Phexe Industries have just released PXi PSVita Theme. This is a theme with six background images, each one with Sidebars and Page Titles. It's really simply to install, just transfer the pictures to your Playstation Vita and select the images you want to use.
Quote from Phexe Industries Blog:
Just made a 6 Background theme for the PS Vita, with Sidebar & Page Titles. Click below for the fullsize versions (Please don’t link directly to the images, instead link to this post)
I have my VITA setup up as so (for use with this theme)
Page 1 – Playstation VITA Games
Page 2 – Playstation Portable Game
Page 3 – PSN / Mini Games
Page 4 – Media (Photos, Videos, Music, Netflix, Music Unlimited, etc etc)
Page 5 – Apps (Facebook, Flickr, Twitter, Web Browsers, Friends etc etc)
Page 6 – System (Settings, Content Manager, Remote Play, Welcome Park)
Let us know what you think of the theme in the comments below!