French beans
I love the purple colour of french beans, though it's a pity they go green when you cook them.
I grew some of these last year, thinking they would be as easy as runner beans, but they need a lot more heat, and very careful watering ( do not overwater!). I also found that they liked to sprout later in the year than runner bean, and needed more sun.
They only grow about 6 feet tall, so its easier to stake them than runners, which will just keep going and going!
Really like the purple flowers, and the big purple-green leaves - makes a nice colour contrast with the runner beans, and the purple beans add an extra little interest in the veggie patch!