Blue Marbutt and Grandma Roberts Purple Pole are good varieties with relatively tender pods.

I grew out both Blue Coco and Purple Podded Pole this year and preferred the latter. This was an unusual weather year for us too - seems to be the new norm.

Violetta tr intifada the Italian purple beans are tender and early

I can vouch for Grandma Robert's Purple Podded, grew them last year they were tender and delicious.

Annette

Ditto on Grandma Roberts; the grandson loved them straight from the vine, and I liked the round pods. It was a prolific producer. I grew Blue Marbutt last year, which also has round pods; but they were
more greenish at snap stage, becoming fully purple as they dried down.

I also grew Trionfo Violetto last year, which has long, flat, tender pods with good flavor... but the yield was disappointing, as it was in a previous year. Kew Blue (which I grew several years ago) is very similar, but had a slightly better yield.

The most productive purple-podded snap bean I've grown so far was Czechoslovakian, obtained through SSE. It has flat Romano-type pods 5-6" long, and bore heavily until I let the pods go for seed.