Instagram.

The closest thing for me to Photoshop on my Iphone is Instagram.  I have literally fallen in <3 with this app.  You can take a picture, change the tone of the color and then upload it to Instagram, link it with Twitter and Facebook.  I have posted just a couple of the pics below that I have taken, changed and uploaded.  The best part of all, It's FREE!  Make sure to download the app, link your contacts and that way you can like or comment on other pics and others can do the same.