Easy Plaid Background

Open a new image:

300 x 300 pixels
Resolution: 72
Image characteristics: Raster Layer
Color depth: 16 million
Background: Transparent

Flood fill with Blue Metallic Gradient:

Add a new raster layer and flood fill it again with the Blue Metallic but changing its angle to 90.

Lower the transparency on Raster 1 to about 60; and Raster 2 to about 40, as follows:

Select your selection tool click then the custom selection button on the selection bar and enter the following settings:

Top: 100
Left: 100
Right: 200
Bottom: 200

Click OK to close the custom selection dialog box.

Select Image/Crop to Selection (Ctrl + R). You now have a 100x100 pixel image with two layers.

Copy your original image (Shift +D). Highlight (make active) Layer1. Select Colors from the dropdown menu and play with the settings. When you're happy with the color click OK. Below is the plaid I made.