You can put most caps on there and you'll see some of the light shine through, but the stock ducky shine caps have transparent legends that you can't really buy anywhere else. More specifically, they're either ABS or POM, painted black, then the legends are laser-etched to remove the paint in the shape of the legend so light can shine through the transparent layer. The problem with this is that the paint will eventually wear off and light will shine through in a blob and you won't see the letters/characters anymore.