We had purple beans for dinner, from farmer's market. I heated some olive oil in a pan and cooked them through until they had turned all green, and then salted them a little at the end.
The recipe called for adding chopped almonds but it didn't happen; instead I served the boys tofu that I had cut into cubes and boiled (boiling it improves the texture quite a bit, firming it up more to my liking).
I don't know which variety of purple beans we had. A search of the net unearthed the "romano purpiat bean" (from Territorial Seed)
60 days. Everything about this purple Romano bean is noteworthy:
healthy robust plants, deep violet stems, lilac blossoms, and lustrous
purple pods. The 5 inch, flat pods are so tender, crisp, and delicious
that we found them irresistible picked fresh from the plant. Cooking
the pods turns them a brilliant jade-green with a nearly stringless
texture. Remarkably productive plants reach 24 inches tall and tolerate
cool, early plantings. Brown seeds.
and Peaceful Valley has the Royalty Purple variety
Phaseolus vulgaris Tender Annual Bush. Purple bushes with
short runners and purple flowers. Bright-purple stringless 5"-6" pods
cook to dark green. Buff colored seeds germinate in cold, wet soil.
Bred by E.M. Meader at the University of New Hampshire and introduced
in 1957.
Why are beans purple? Good question. I got as far as finding this:
Genetics of flower and pod color in Phaseolus vulgaris
Christian A. Okonkwo, and
Carl D. Clayberg
The Journal of Heredity 1984:75(6):440-444© 1984 The American Genetic Association 75:440-444
A new locus,
Prp (
purple pod), having five alleles affecting
anthocyanin pigmentation of corolla and pod, is described in
Phaseolus vulgaris L. The allele
Prp produces dark-
purple corolla
and is fully dominant in this respect over the other four alleles
that determine light-
purple corolla. In the absence of Ro,
Prp is responsible for medium-
purple pod when homozygous and light-
purple pods in combination with the other alleles. The alleles
prpsh2 and
prpsh give green pods shaded with
purple and are codominant
with the
prpst allele, which causes green pods to be striped
with
purple. These four alleles are dominant for pod color over
prp, an allele causing green pods when homozygous. The interaction
of these alleles with the genes
Gri, V, and
Ro, which also affect
anthocyanin pigmentation of corolla and pod, is described. No
linkages among these four loci were observed.
That's from 1984; I don't know enough about bean genetics to go any further.
(Oh, and they are delicious.)