TL;DR: most of the dyes available are some variant of yellow-beige-orange with alum and green-grey with iron, which is pretty typical of any given sampling of plants (that's by far the most common category of vegetable dye). The brightest yellows are probably from pomegranate husks, mango leaves, and chicory, with alum for all of those, the best green is probably from Chicory with iron, but I know you can get a good green from fennel greens with iron, so I might have to look into relatives of fennel, like carrot greens with iron. The best orangey color is probably from persimmon, but it's not very bright. Perhaps carrots or carotenoid rich yams might be made to work. With a good red, orange could be made from a bright yellow, but aside from beets, I can't think of any in the real world plants we currently have on hand. Blues can be gotten from black beans, if those can be included under the category of string bean (same species), but we don't have any indigotin sources in game yet, and I think our only good blue is dimple cups. Purples can be gotten from beets, which doesn't work well, or from lichens which haven't been added, or snails which haven't been added.
Banana sap (and presumably Abaca) - brownish to reddish, from tannins. The Fe'i banana is apparently used for a reddish dye. One source suggested it is useful as a mordant for other dyes, which is typical of tannins, though of course they also contribute their own color.
Coffee - browns, from tannins
Guava - pale rosey brown with alum or no mordant, slate grey with iron mordant (as with any iron mordant, this will be destructive to protein based fibers, making them scratchy and brittle) [
source]
Rambutan - can be used to dye fiber a sunny yellow, using alum I assume [
source]. Iron will give greys or greens. "Young shoots are used to dye yellow silk to green. A dye called
ayer banyar, made from rambutan leaves and fruits and combined with other ingredients, is used for dyeing red silk black." [
source]
Tea - has been popularly used to make reddish browns, especially for making paper look old. Iron mordant will give dark greys
Avocado - beige yellow from fruit skins, beige rose from pits, no mordant [
source] or pale rose pink, no mordant [
source]
Pomegranate fruit husk and pith - beige brown unmordanted, intense mustard yellow with alum [
source], as usual with yellow dyes, darker greys can be achieved with iron, at the possible expense of fabric softness
Cherry bark, also apple, apricot, peach, plum, and any other fruit tree in the rose family - creamy yellow to rose pink with alum or no mordant [
source], greys and grey greens from iron
Persimmons (unripe fruit) - somewhat brownish earth toned rose [
source] probably grey with iron
Walnut - a very deep intense chocolatey brown, very wash and light fast [
source] This dye was widely used because it fixes very well to most fibers and has the benefit of being somewhat toxic, so it inhibits insect damage (though not at all dangerous to wear)
Black Beans (not mentioned, but a cultivar of Phaseolus vulgaris) - a nice strong blue, like a slightly less intense indigo, alum mordant [
source]Beets - magenta red, more or less what you would expect from the color of beet juices, mordanted with vinegar. Color can be adjusted by varying pH, but the solution must be acidic for the dye to bind to the fiber. [
source] Presumably you could also vary the color by starting with differently colored beet cultivars. I have my doubts as to the light fastness of this dye, as according to wikipedia, betanin, the primarily pigment molecule, "degrades when subjected to light, heat, and oxygen" [
source]
Carrots - I don't know about orange carrots, I don't think it works well, but apparently purple carrots give a very nicely colored purple dye [
source], but I have strong suspicions about wash and lightfastness
Chicory - mustard yellow (alum), yellow-green (copper), bright yellow (tin), forest green (iron), creamy biege (no mordant). There are reports of a blue dye from the leaves, but this seems to be untrue. [
source]
Onions - give a nice warm orange yellow from the skins