Wave
You'll need a version on photoshop, and a color scheme or your choice.
Step 1
Make a new image. I'm doing mine 20 x 600. With my 4 scheme.Step 2
Use 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 3
Take the selected section and make a new solid color layout with your first color.
Step 4
Duplicate the layout 3 times (4 for a 5 scheme) Fill each layer with each other color.
Step 5
Match your settings like mine
Final
And 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.