This colouration is fine. There is nothing wrong, it is not stress induced or a deficiency of any sort, it is just a genetic quirk of this particular plant. It may continue this throughout its' entire life or it may even become more purplish with completely purple leaves, or even go away all together. Do not be worried, there is nothing wrong with your plant, in fact the purplish colouration is quite common.
Hope this helps,... Organoman.