Varies on plant and light source, as well as airflow, etc.
Is the plant too close, too far, or the right amount of distance from the lights?
Up nitrogen content a bit, I have seen many various purple kush strains, but that looks like classic nitrogen deficiency. If new growth is green stemmed, try increasing nitrogen content slightly. Keep using a higher nitrogen content fert until a week or two into flower then phase down to a high P-K content fertilizer, and all but eliminate nitrogen, till the last couple 2-3 weeks, then go straight high P-K with little to no Nitrogen.1/4 strength Fox Farm nutes for both plants today. temps got up to 88 F. I know this is a purple kush but do the stems have too much purple in them? View attachment 920102