Use Photoshop filters to create the ever popular grid.
Step 1 Create a new document (Cntrl+N) 256x256 pixels, with a white background.
Step 2 With Black set as your foreground color, go to Filter > Render > Clouds.
Step 3 Next go to Filter > Pixelate > Mosaic. Use 32 as the cell size.
Step 4 Now go to Image > Adjust > Auto Levels.
Step 5 Select Filter > Stylize > Find Edges. Or you can choose Glowing Edges. There you have it. You can change the color by adjusting the Hue/Saturation.