Blue pigment

The blue in an LCD color filter is copper phthalocyanine, the same molecule as phthalo blue paint, in one particular crystal arrangement. Its industry name is Pigment Blue 15:6, and the arrangement is called the epsilon form.

Copper phthalocyanine molecules are flat, and in a solid they stack like plates. They can stack at several different angles, and each stacking gives a slightly different shade, because neighboring molecules affect how each one absorbs light. To get the epsilon form, makers grind or dissolve the crude pigment under carefully controlled conditions, for example milling it with salt and a solvent, so the crystals settle into that arrangement. The salt is washed out, leaving particles well under 100 nanometers across, small enough not to scatter light.

Epsilon blue absorbs red and green light strongly and passes a clean blue, which is what a display needs. It also holds up well to heat and strong light. In the color filter, it's dispersed in color photoresist and patterned into the blue windows. Makers usually blend in a little violet pigment, often dioxazine violet, to bring the color to the exact blue a TV standard calls for.