I always Start from clone so I can't help. Her has seedlings that are so yellow they are going white anyone had this happen. Could he have to much light on a seedling
pictures but if its white or a light tan color, wait, my last one did it and it will change colors to green, it will take time and ph water to 5.5-6.0 really key on the ph. not to much water but she will green up.
Patience is key to successful growing.If its just the cotyledons,it'll grow out of it.It was already recommended to check water ph,just don't water too much.I think too soggy of a medium can cause yellow or whitish coty's(birth defects).GL