The same thing is happening to me , I'm at day 23 days old from first sprout (using happy frog soil) I'm growing sour diesel n noticed today that the three bladed leaf stem is like a purple color ... The main stem and top stem is a light green but idk y the stems goin to the fan leaf are purple ..... I haven't given them nutes yet, just transplanted it from solo cup to 3 gal root pouch, so I gave her pure water and next in two days I'll give her nuts(flora nova, grow) for the first time, I hope this will help , is this something I should worry about? The next nod up is beautiful green and I toped it for the first time at the 4th node. Could this have caused the stem on my fan leaf to turn purple? Any advise would b a big help.
Thanx, GrOw TiGeR