Add shadow, but just a bit. And coffee beans have a little bit of shadow on one side of the "line" that you've drawn in the center...I suggest using the same colors you used for each bean only adding a small little bit of a darker color...the last one, you could use a tiny dot of black and mix it with the same color you have on the bean and then draw a second line flush against the first one you've drawn. You could add a little shadow behind them too. That would make it stand out a bit and still let it be the same design.
Hope that helps a bit. That is such a CUTE cutie mark, btw!
Love coffee themed ponies~