Trying living soil.. indicator of nutrient needs?

My first year gardening solo and I’m trying to generate and follow living soil practices. Very new so it’s not an exact science (nor will it ever be knowing my brain) but I am doing my best to pay attention. I transplanted these marigolds a few weeks ago and last week I noticed that the leaves are turning purple. What can this an indicator of? I’m worried about nutrients as it seems as though other transplants in my bed aren’t taking off as I thought they would. Bok choy bolted. Lettuce is growing so slowly I haven’t been able to harvest any despite it being one of the first things I put in in mid-March. Chives are doing amazing though! Perennial at this point. Zone 8a/b.