I have seen light tan, medium tan, and darkish brown moonflower (Ipomoea Alba) seeds. Is there any difference? Does one plant only make one color of seed? My packet this year only came with light tan ones, so I do not have a picture of the different colors. In the past, my packets have come with a mix of seed colors.
I'll share what I'm aware of regarding the seed color and flower color of Ipomoea alba.
I am aware of only 2 seed colors that relate to different strains with somewhat different characteristics.
The typical white flowered form produces light , medium and some darker brown seeds and these typically produce heart shaped leaves.
There is a black seeded form of Ipomoea alba which produces white flowers and typically multi-lobed leaves and the black seeded form seems to be somewhat more cold hardy...the pedicel surface is rough as compared to the smooth surface of the pedicel produced by the light seeded form.
The dark seeded form was available many years ago and was offered in the 1932 Park (?) seed catalog and is still available from some veteran Morning Glory enthusiasts.
There seems to have been a light blue form of Ipomoea alba offered years ago by the seed companies as it is described in some old catalogs , on seed packets and visible on some rare photographs.
I have been trying to track down the missing blue colored form of Ipomoea alba...it seems to have been growing in Texas a few decades ago and in Florida...the blue form of Ipomoea alba was reported to be sensitive to cold , perhaps even more so than the white flowered form.
I agree that the seed color is a general indicator of the flower color in that light seeds tend to produce light flowers and dark seeds tend to produce darker colored flowers , but not always.
I responded to an e-mail request to post here, although I'm usually more often found on the GW and my own 2 groups devoted to all Morning Glories (i.e.,Convolvulaceae).
Hope the info I shared is of some help...
Because you've bought only one variety of Ipomea seeds, they will all be the same colour, because they'll only produce a particular colour flower. Generally, if an Ipomea seed is dark, the flowers it produces will be dark (say, purple) and if they're light (peanut butter coloured) they're likely to be pale (pink, possibly). So your suggestion is accurate - the seed colour, to some extent, hints at the colour of the flower.