Thats because colors on a COPO did not require any input from engineering, you could have ordered a COPO in any available color the line had, and got a normally coded trim tag, or your could have ordered one in any color GM had available and you got the - - trim code same as any other Camaro built. The ZP2 option was for the color blind people that wanted a red interior in a frost green Camaro, or any color code GM felt was outside the allowable combinations. GM did have a list of colors that you could have for any given exterior color, stray outside of that list and your window sticker got the ZP2 option code on the window sticker. If GM felt that white was not an acceptable interior for use in a green car, it would not have been on the "allowable color combinations list" in the Camaro ordering book the dealers had. If a buyer really wanted a car built that way, they had this process for overriding the color combinations and you got your requested interior color. Just eed to find that list in the dealers order book.