This triangular pattern will be pinned to the document edge so point 1 will be repeated on left and right and top and bottom. Use guides to aid in this.
Tutorial by: Andrew Buckle
Works with: Photoshop CC and CS and standalone, Elements
Other tutorials: Tutorial links
Videos: Video tutorials
Go to the view menu and new guide layout. I am using 10 x 10 guides but you could do the same with 15 x 15 etc 4 x 4 or so on. Once the guides are in place. Go to the pen tool. Set the option to 'shape' (not path). Set the color
Click one of the guides that cross the edge of the document. Now go to another point along the edge (either direction) and click at another guide intersection. Now click in the center (or offset from the center) at another guide intersection to create another anchor point and then go to the first point. Now the shape layer is still selected. You can de-select it via the layer panel or you can avoid accidently removing anchor points by going to another guide intersection (along the same edge) and click a new anchor point and then go to the same central point and click again to create a new point for the triangle. Then go back to the first triangle's second anchor point (on the edge of the document) and add a new anchor point and then go to the start point for the the second triangle. Go to the fill dropdown and select a new color. Repeat this over and over for as few or many of the guide intersections you want to use. Set the color to random colors or perhaps alternating colors or all blues or all reds or red and green etc.
The guides for the triangle are also useful so you can match the anchor points on the left and the right edge as well as the top and the bottom. So if you create a point at the intersection of the 3rd along the top then you can also create an equal point at the 3rd intersection along the bottom (and the same for the left and right). If you want to have no obviously jarring structures (like the one below where the pink and pink match in the top and bottom halves then should try hard to use totally different colors throughout so one side should go with yellow and the other side with blue and not two blues together)
One with two pinks clashing
One corrected with totally random colors for the square
Once you have created all the paths (you can have as many shape layers as required) then you can flatten the layers and edit menu define pattern.
You can unflatten (just go back in the history panel) and select the central point by using the direct selection tool and move the center for the triangle pattern. You can duplicate the triangle pattern and re-color that and apply transformations such as rotate and then combine using blending modes or opacity. You can apply effects to central part of the artwork such as a twirl (use selections). You can add adjustment layers to the mix and re-color using color lookup or photo filter etc and then define those as a pattern. You can create multiple layers of the triangle patterns and then set different scales such as 50% etc and blend those to create more fragmented jarring imagery.