This is a fairly representative set of colours obtainable from British dyestuffs.
It doesn't include the fungal or the lichen dyes. Those plants are often under threat, and these hoops were made to demonstrate in public. I didn't want to encourage the use of rare plants.
These are all on wool, if I use linen or cotton then I need to change the mordants, and mordants are all toxic to a greater or lesser extent.
Again, I was demonstrating in public so all of these dyes are simply alum, iron and copper mordants which are the least toxic and safe to be disposed of, with care, in the sewage system.
I know that if I used Chrome (which causes feminisation of the invertebrates at the lower end of the aquatic environment, and the concommitant damage, etc., ) or tin, which creates organo-metallic toxins that are persistent in the environment) then yes, I can get brighter, sharper colours.
But, to be honest, I don't think anyone can call themselves a 'natural dyer' and routinely poison the environment when I can get this range without doing so
That range of colours shown in TeeDee's first post is very do-able, very realistic, especially on cotton/linen.
M