Biskopens is a good one, with the 'green' peas having a purple tinge. I've got some very purple peas among my Kent Blue this year, with a fair few purplish ones. It's quite striking, so I'll grow them out separately next year and see what happens.
I am doing my best to cross the pure purple seeded variety Purple Passion to any other peas that are flowering. I attempted to cross one flower onto a depollinated Sugar Magnolia, but i only had one flower to work with. Purple passion produces full size pods on tiny very frail pea plants, and every time i plant it i get less seed than i started with. I only have two pods that set maybe with 5 seeds each. I will also try my best when biskopens the pure red seeded pea begins to flower. I believe salmon flowered and maybe sugar magnolia will still have some flowers by then. That is the best i can do. It will probably be several generations before i will know if i succeeded.
my experience so far with Dwarf Grey Sugar Pod peas has given me some fully dark purple peas, but they did not repeat. it's ok. i like peas anyways. the dried DGSP peas are not as edible as some of the others but they are very prolific here and grow easily, we also like the colored flowers. i grow a mix of other peas too given to me by various sources that i have not kept segregated other than by appearance of the seeds. i can usually pick all the DGSPs out because of the seed size and shape. i have Wando, Alaska, and some others in the mix, but i can't say exactly which any more because some of them just don't do much here so perhaps they have not made it past some bottleneck year in the garden. the smooth green soup peas with the hypertendril trait are also an easy pea to pick out in growth habit, but the peas themselves are also somewhat distinctive enough for my purposes.