To get reds and purples in peas, the starting gene is A, a dominant gene that controls anthocyanin production, responsible for many of the blue purple and red colours in plants. Other genes turn on the expression of this in various parts of the plant. And some genes turn it off, even when the plant carries A.
Why is this important? To get a stable line of coloured peas, having A contributed by both parents means you don't have to search for it in the offspring - every child plant will carry AA. So when I cross a Purple Podded with a snow pea, if the snow pea carries A, the numbers of crossed offspring i need to grow in subsequent generations is reduced. I only have to search for the other genes. This will influence the grow out strategies in future seasons.
A normal indicator of A is purple or red colouration somewhere in the plant - the leaf axils, the flowers, the sepals, or even the seed - if they are red or purple or brown, then the plant carries A. For example, my Golden Podded pea has yellow pedicels and sepals, but I can tell it carries A because it has purple leaf axils and petals.
But there are lots of genes that influence colour of flowers and other bits, some acting alone, others in combination with other genes. A bit of a search on the John Innes database showed the following possibilities, amongst others
Genes am1 and am2 inhibit colour expression in flowers even if A is present.
b gives rose pink flowers and an effect on axil and seed coat colours, and axil pigmentation is reduced from purple to red. For example, the Golden Podded above looks a bit reddish to me - must compare with some others I've got growing.
Cit gives a citrus yellow flower - interacts with gene Cm to give "a light dull ocher with faint salmon hue."
cfg gives greenish flowers, and rub gives brick red wings on the flower.
So lots of material to play with out there.
Unfortunately, all of my lines so far have either purple or white flowers - will have a close look over the next few days to see if there are any of these aberations lurking in the patch.