Firstly create a new image in the size of your choice.
Next, press D to reset your colours.
After that go to Filters -> Render -> Clouds
Then, Filter -> Stylize -> Find Edges
Now invert the colours by pressing CTRL + I or going to Image -> Adjustments -> Invert
Then go to Levels by pressing CTRL + L or going to Image -> Adjustments -> Levels
In the Dialog Box, set the Input levels to about 0, 1.00, 35
Basically just fiddle with the settings till you're satisfied.
Then to colour your image, just add Hue/Saturation.
Add Hue/Saturation by either using CTRL + U or go to Image -> Adjustmensts -> Hue/Saturation and check the colorize box, then just fiddle with the Hue, Saturation and Lightness, the Hue will change the colour, while Saturation will change the amount of colour and Lightness will change the amount of light.
Then once you're finished you should have an image similar to the one below.
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