Purple is correct, evn though the spider plants may revert or change/vary the variegation, genetically, they are still that variety, so if a reverse variegated spider plant turned plain green, it is not getting enough sun and will change back apoun recieving what it wants. The plantlets also can occasionally temporarly change colors. Spiders grown by seeds are going to be either green or white, the latter dying from lack of chlorophyll
