Easiest way to build an interchangeable wardrobe? Stick to basic colour schemes. For me, this means black and white. Easy to add pops of colour, if needed, but it's not always needed.
This dress is striped, but with shift in the line pattern down the front. But add a topping dress, and it gives the illusion of a checkerboard. Obviously, I had to add the checkerboard socks... but those were hidden by boots.