Good question. I've heard speculation that it's due to several different operators leasing/running the table games over a period of time. A different color for each operator to track his play. Don't know if this is correct for California Club, though different color chips for different lease-operators did occur in other casinos.

Perhaps a downtown LV expert can shed more light.

These are nice looking C&J chips. Used to be rather easy to obtain, at least most of the color combinations, but even these have become more difficult to find at reasonable prices anymore.