Begin by creating a new document—the example is 128x128. Choose a light blue shade for the foreground color and a dark blue shade for the background color.
Now, go to Filter » Render » Clouds. Press Cmd+F (PC: Ctrl+F) several times until you get the clouds the way you like them.
Next, we will make the “Neon Lights”. Go to Filter » Artistic » Paint Daubs, and fill in the following values: Brush size: 40, Sharpness: 36, Brush Type: Sparkle.
That’s it! You now have your neon texture—to make it seamless, go to Filter » Other » Offset, set it to Wrap Around and half the dimensions of your image. Use the Smudge Tool to blend the edges where you can see a seam.