Lemon plant that looks sick to me.
Having a compost setting like mine, lots of seedlings tends to germinate and grow. As I don't have the time and expertise to grow these seedlings, I tend to crush them - sorrily - and mix with the compost.
Once in a while, there are certain seedlings, depending on my mood, I left alone to grow. Usually they grow on the edges of my composting pails. So it's okay to let them be. If they die while I'm moving the compost around, then so be it. No loss for me -I always think that composting comes first - to clean up my kitchen wastes.
When some seedlings managed to survived on the edge of the pail, that's cool. Like this little lemon plant, I'm guessing this is a lemon plant. This one survived growing on the edge of a composting pail. It doesn't seem to mind me raking beside it to move around the composts. When it's around 12 inches tall, I decided to look for some pots and use some of the composts to place this lemon plant on its own pot and moved it somewhere it gets some direct sunlight during daytime.
I'd like to believe that this lemon plant is doing well, except that the leaves has this yellowish color. I don't plan on doing anything on this plant except water it as often as I could.
I read online that this might be some kind of nutrition deficiency or illness. That's about all I could make out of this.