I'm growing peas in a coffee tin. I noticed some discolorations showing up on the leaves. Can I get an early indication of over or underwatering from this feature, or is it entirely natural?
In my opinion, you are doing right. Your peas show beautiful leaves, well-built and solid, which means they are not underwatered. And if they were overwatered, this would give easily rise to a fungal disease, which is not.
Thus, from the photos you've posted, it seems to me that your pea watering is good.
The white lines you see (in my opinion) are caused by a tiny beetle that eats the leaves from the inside. (Liriomyza gender, L. huidobrensis species)