In my opinion newer growth is always a bit lighter than the rest. If your ph is good you can always add in somemore of the trace nutes, if your worried about it, but they do look like they are trying to darken up and normally deficiencies normally start at the bottom and work up. I’ve also been adding great white enzymes every 1-2 weeks and b-52 vitamins every feeding, It seems to help a lot even things out.