Well, there's a black walnut for dark browns and blacks, woad for blue, weld for brown, pokeweed for pinks and purples, Siberian iris for pale blue, persimmon (fruit) for pale orange, rhubarb for medium pink, elderberry (fruit) for dark wine, sumac (berries) for rosy purple. These all work well for linen and cotton (magnesium mordant) but need to be copper or magnesium mordanted for wools.

I've grown woad, weld, madder (mostly to dye wool) and Hopi red dye Amaranth and bulls blood beets as red food dye which work really well. I usually grow safflower just for show but it can also be used as a red dye and although I grow saffron crocus, I prefer it in food and getting enough to dye anything yellow would be really tough. I have oak trees but I've not tried galls yet for brown. Mostly the stuff I do is with alum as a mordant.

Based on Regenaf's post, I should also try elderberry and rhubarb since I grow them too but never thought to use them.

How many of those listed are really considered "herbs" though? some are trees, iris's aren't herbs... ?

They are all herbs. Many members of the iris family are herbs - think of Orris, Yellow Flag, Blue Flag.

Herbs can be trees. Think of an elder tree, an oak tree, a bay tree, a willow tree, a eucalyptus tree and lord knows how many other trees.

Size doesn't matter when it comes to being a herb!

Here's my list (still not complete) of dye herbs. I've grown most of them over the years, but never used them for dyeing:

Agrimony, Alkanet/DyerÂs Bugloss, Almond, Amaranth, Angelica, Asparagus, Beetroot, Bugle, Burdock, Calendula, Chamomile, Chicory, Cinnamon, Coffee, Coltsfoot, Comfrey, Dandelion, DyerÂs Chamomile/Golden Marguerite, Elder, Elecampane, Eucalyptus, Fennel, Fenugreek, Feverfew, Foxglove, Fumitory, Goldenrod, Hawthorn, Heather, Horseradish, Horsetail, Indigo, Juniper, Kaffir Lime, LadyÂs Bedstraw, LadyÂs Mantle, Madder, Marjoram, Meadowsweet, Mugwort, Nettle, Onion, Pear, Pineapple, Pokeweed, Purple Cabbage, Red Clover, Rose, Rosemary, Safflower/DyerÂs Thistle, Saffron, Sage, Sassafras, St. JohnÂs Wort, Sunflower, Sweet Joe Pye, Sweet Woodruff, Tansy, Turmeric.