Astor's Fashion Studio fall collection is 6/9 about duochromes and multichromes, which are a rarity in drugstores in general, but actually nicely shifting duochromes are even harder to find, even outside the drugstore. I picked up three shades that drew me in, and let me tell you, these are great. Let's look at them together, shall we?
Swatched over black, with top coat. Do you see that shift? Wow. I originally wanted to swatch it side by side both by itself and over black, but noticed that it's quite sheer on its own, so I went for the "over black only" approach. The number of coats you wanna apply really depends on if you can make it nice and smooth with the first or if you have to fix up a few spots here and there with a second coat. Also, you can pretty clearly see brushstrokes here.
Swatched over black, with top coat. Cooper King on pointer and ring fingers, Crystal Blue on middle and pinky fingers. That shift is AMAZING! Wow. Look at that last picture... Once again, you may need two coats to make it nice and even. With all of these, the effect will be more apparent with more (sun)light hitting all the shimmery goodness.