You'll need a version on photoshop, and a color scheme or your choice.
Step 1Make a new image. I'm doing mine 20 x 600. With my 4 scheme.
Step 2Use your rectangular tool and make a rectangle all the way down. since my image is 20 in width and i'm doign 4 colors my rectagle for each color will be 5.
Step 3Take the selected section and make a new solid color layout with your first color.
Step 4Duplicate the layout 3 times (4 for a 5 scheme) Fill each layer with each other color.
Step 5Match your settings like mine
FinalAnd you're done
You can also do this vertically. Just reverse the numbers.
Ever better you can make triangles too. Instead of cliking sine at the top click triangle.