Combination of lenses made from materials of different refractive indexes, constructed in such a way as to minimize chromatic aberration (which in a single lens causes coloured fringes around images because the lens diffracts the different wavelengths in white light to slightly different extents).
Blue stands for the Pacific Ocean and water on which life depends. Yellow symbolizes the sun. Green represents the lush vegetation. Effective date: 18 November 1977.