Oscar Diaz's RGB Vases look much nicer nested together than apart.
Each vase is made using the values of red, green and blue that make up the specific purple color (P242). When the three vases are nested, the light passes through, and mixes the three colors so that the purple becomes evident.
A computer is used to calculate the exact amount of color that each vase must have in order to achieve the desired color.
RGB Vases [Design Milk]