Bragg Diffraction in Christmas Tree Colloids

In the pictures you can see a colloidal crystal of particles with a diameter of 550 nm. The particles have a gold core (15 nm), a fluorescently labeled shell and an outer silica shell.

The crystalline structure of the crystal is random hexagonal close packed. In the crystal you can see Bragg diffraction and so depending on the angle of observation the crystal acquire different colours, in this case a Christmassy green.