Leaf discoloration?

Absolutely fine with no issues. Give it a chance to grow before doing any sort of interventions, she is just a new born baby and still finding her way in this world. Doing anything radical to such a young seedling is likely to cause more issues than solve any perceived or imagined problems.

Looks fine to me. Stonington Blend is 40% sphagnum peat moss, coco fiber (coir), composted manure, perlite, fertilizer (see below) and mycorrhizae. mainly peat vs coir. its a soil mix with all the manure and fertilizer in it. npk .50-.32-.12 Derived from: Composted poultry manure, fish bone meal, lobster & crab shell, kelp meal, earthworm castings and alfalfa meal. I Wound not worry to much about it. could always sprinkle on some magnesium into top soil or mix it into the water. this mix should last you till about week 3 or more after that it may need amending, autos feed light. guessing its an auto as you are starting it off in a 5gal pail vs transplanting it from smaller containers. Can't find a breeders page for that brand/strain. Good Luck!

Hey Growmie, Looks like the seedling is showing the first signs of a magnesium deficiency, did a little research and it seems Stonington is coco coir based, and having calcium/magnesium deficiencies is quite common when growing in coco just add some type of cal/mag supplement when watering and it will fix the problem. Hopefully, this was helpful, and remember ... "Happy Growing" and "Free your mind one puff at a time".