Discolorations on Lone Leaf

I believe the answers already here are correct for the most part, the discolorations are signs of slight Iron (Fe) deficiency! your plant needs to be transplanted into a bigger pot ASAP!! this small solo cup may be nice for seedlings but once the roots will grow out of the cup instead of being air-pruned (which is what usually happens with fabric/smart pots) they will start to rotate at the bottom of the cup and bind themselves. This inhibits ALL nutrient uptake which is probably why the early signs of deficiency. No special fertilizing needed just transplant her to a bigger pot (I always prefer straight to the final pot to reduce root damage) then give her a nice nutrient rich irrigation with at least 20-30% runoff and keep going with your current schedule and setup. If this problem persists after all of that then upload another picture here to determine what else may have caused it. Hope this helps! Good luck and happy growing :)

If your ph is in check and it's not spreading at all then you have already corrected whatever was causing it. Bigger potter for sure very soon. Looks like it might be a start to nute burn if it spreads. Hard to say it's very early. Good luck and happy growing 🌲🌲🌲👊

Everything looks good bro get it into a bigger pot and shes good to go👌👌

Nothing to worry about yet, unless it starts spreading. That said, that plant is very close to or already root bound. Time to transplant. Also, try not to let the leaves get wet, it'll almost always cause more problems than it fixes.