Not sure about the color change...

So this started 2 days ago. Its spreading very slowly on the tips. Started with just the largest blade and it had the white appear on that tip at the same time as the purple. These are in coco and im using LEDs. Temps stay around 78F all day, and get down to about 71F overnight before a heater kicks on and raises the temps to around 84-85. Dont think it would be a deficiency this early? pH is around 5.7-5.8 when watering.

Its burnt either from the soil or the heater kicking in, get rid of the heater, dropping to 71 is ideal, flush and hope it comes back.

if tips r white not yellow/ brown ur not overfert at all its signs off mag diff/phorsous give 1/6 reg dose nutes n they come round fine , get temp down 75noalso if kept at 80 degrees ,low N HIGHER p,K ull get higher rate females well neg diff will keep ur nodes much tighter higher as she grows night temp 1-2 degrees thats all

seedlings that young don't need to be fed.

look at those poor girls im talking bout r.o. water mixed 150ppm or less of balanced nutes,less than the water at ur tap n probly less than its being givin now unless using disstilled/r.o.water (it was never said so) if tips r white not yellow it will only progress im sure but im new to this only 18 years experince and medical liecense holder,but to each thier own