You really should fertilize if you want a healthy productive garden. It makes a world of difference. Your beans are starving as evidenced by the dark green mottled with yellowing and the almost white leaves with green veins. I don't know how many beans you have produced but if you had fertilized I can guarantee it would have been a lot more. I am a strictly organic vegetable gardener. I recommend using only organic products in the garden whether it be fertilizer or fungicide. I would start using a pelleted dry fertilizer on everything. I would also go to the Organic Gardening thread on this forum and start reading it from the beginning. You will learn a lot.
Leathery and dark is normal for bean leaves that are well past peak production and are likely in decline. The oldest leaves do that prior to a normal decline.
The leaf showing below those in the photo has some rust on it and is showing stress...a sign of fungus. Since you have already gotten good production, I wouldn't do anything to these. Bush beans don't have much of a life span after peak production....at least those I've grown for decades. You will need to rotate your planting next year and keep a close eye out for the rust.
I'd say well done on your first attempt and enjoy the produce.