I created a set of Subtle Seamless Geometric Pattern for you to download for free in .PNG file format. I reduced the contrast for each of it and scaled into 3 sizes. There are 5 different geometric style with 10 color alternatives, so basically you can have 150 total number of patterns to choose for your design.
I wrote a quick tutorial of: How to Define Pattern as .PAT File in Photoshop if you still do not know how to put digital modern pattern into a design.
You can check the demo page for quick preview of each geometric pattern style in different sizes.