I found a vintage post card I liked and took colors from it in Photoshop. I created stacked rows of colored squares using the photoshop square brush set. Then I duplicated the layer. The duplicated layer is on top. I pulled that layer up diagonally. Then set it to "multiply". That is how you get two perfectly matched dark and light colors.
Color Attribution:
lacebutterfly(Palette License: CC0. Contact image author for image licensing.)