If you have one of Cut Cute Crafts square window box templates, then this is for you. The video with the assembly of the two sizes of the box templates is up and you can watch it in addition or instead of the pdf guide that comes with the templates.
As you can see in the video, the bigger size box is made of two pieces of cardstock. It is a great way to make a two color box. If you want to make a smaller box in two colors, it can be scaled down easily. Just make sure to select all elements of the box and scale them together.