No, peat moss and perlite isn't a good grow mix. Impossibly acidic.

Almost anytime you see purpling on a plant whose phenotype isn't noted for the color, it's a phosphorus deficiency. Now, that can be exacerbated by cold temps, but it's still a symptom of low P uptake. More P or warmer temps will fix it, unless you just want the purple bits.
ohkelly Reviewed by ohkelly on . Seedling is Yellowing! The only survivor of the damping plague is now yellowing. He is in different soil from the others which is maybe why she's survived this long. Now she's starting to yellow can anyone help diagnose the problem. Rating: 5