I found an app called Notched for 99¢(I think) & it has the ability to put one or 2 color borders on a wallpaper !! Very easy to use, lots of colors to choose from AND when you upload a wall to the app to add a border, the app detects the colors and will apply one compatible or you can choose a different one off of the color chart offered.
I used a double border on this wall, baby pink & lavender.