Making Your Own Duochromes is Not Possible
You can make colors that shift or shimmer, but those really complicated colors that go from red, to green, to orange and everything in between, there is no way to mix those by hand in your home.
The reason has to do with how these products are manufactured.
Here is one way to think of it.
#1: Imagine you have a sheet of clear glass. If you shatter that glass into small pieces, and then toss in some blue pigment and stir it all up, what you will get is clear glass pieces that are covered in blue pigment. When the light hits them, it reflects blue.
#2: Now, imagine you have a sheet of clear glass. One one side of the glass you paint it blue. On the other side, you paint it yellow. In between the blue and yellow paint, you still have the clear glass. Now shatter that. When the light reflects of this pile, it reflects off the blue, and then off the yellow and it also goes into the sides of the pieces, through the clear and up through the blue and yellow, and so forth. Lots of opportunity for light to bounce out different colors to your eyes.
When you try to mix a duochrome at home, you are doing the same things as #1 above. Just coating one color with another.
When they manufacture Duochromes, the companies use the idea that is described in #2, and it involves layering during manufacture.