Well, depends on what shade of green etc. you're talking about.  I've seen some brilliant green wools, and there's evidence for green linen and cotton as well.  Here's an excellent article on medieval dyes; the same technology would have been inherited, and improved on, by the 17th and 18th centuries. For more on 18th c. dyes, see this article, and read

Liles, J.N.. The Art and Craft of Natural Dyeing: Traditional Recipes for Modern Use. Knoxville, Tennessee: The University of Tennessee Press, 1990.

I think the reaction against bright colors stems from a couple of things:
a) Hollywood -- which clothes extras and commoners in movies in drab colors so they fade into the background on-screen, and
b) the mistaken idea that vegetable colors were drab, when in fact you can get vibrant colors from natural dyes, though you might not be able to get neon green or mauve.  You have only to read the runaway ads in the Pennsylvania Gazette to see that ordinary folks wore lots of bright colors. Keep in mind that the period clothing you've seen in museums are a couple hundred years old by now; of course they're probably faded from wear or exposure to light. Didn't that black (or red, or blue) chemically-dyed t-shirt you bought several years ago fade, too?

Some chemical dyes are more fade-resistant than other chemical dyes; and some vegetable dyes are more lightfast than other vegetable dyes. For instance, the blue from indigo (the active chemical, indigotin, is still used to dye denim) resists fading when exposed to light, whereas the blue from logwood is notorious for fading quickly. Moreover, redyeing old clothing to give it a new look was a common practice.

In addition, most dyeing wasn't done at home.  The popular misconception that most of the clothing worn in the colonial period was homespun and hand-dyed is far from true.  The inventories of ships bringing fabric into ports like Philadelphia show how much fabric was imported; and ads in the Pennsylvania Gazette show that even locally produced fabric was frequently professionally dyed -- in a multitude of colors.

Modern home dyers usually aren't able to replicate the processes used by 18th century professional dyers:
a) Professional dyers used very large vats with rollers, allowing the fabric to be dyed without "crowding" in the vat.
b) Most hobby dyers are dyeing on an occasional basis rather as their full-time job, so they see the time spent on various steps (such as the three-stage process for mordanting linen) as "too difficult", when in fact it's merely time-consuming.

A friend of mine sells knitted caps.  The most common documented color of 17th and 18th century knitted caps was red.  However, when she knits red caps, they don't sell, because guys think they can't wear anything but... brown.  Brown caps sell like hotcakes.  Folks, this is NOT RIGHT!  Yeah, brown caps were worn, but when the reenacting community is wearing ONLY brown caps, rather than a nice mixture of red, blue, green, black, and other colors, we're being inaccurate.  So buy some non-brown caps, PLEASE!

Lastly, many people think that colorful clothing was out of reach for common people in the 18th century. That's simply not true. There was a thriving trade in second-hand clothing in the 18th century; and servants also received cast-off clothing as part of their wages. Look at Pennsylvania Gazette runaway ads for examples of some very vivid clothing worn (or stolen) by runaway servants. If you're doing a lower-class impression, why not have a colorful item that's about 20 years out of date and well worn / patched? You could also have a brighly dyed silk handkerchief, since pack peddlers sold cheap silk handkerchiefs and ribbons.

A particular misconception is that linen is hard to dye in any colors other than blue or brown. This is because linen doesn't take dye (even modern chemical dyes) as well as wool, but also because linen and cotton both require a three-step mordanting process (usually alum-tannin-alum), and most modern dyers aren't that interested in putting that much time into their dyeing. However, there is plenty of evidence that linen was dyed -- by professional dyers -- in colors other than blue or brown in the 18th century. Runaway ads in the Pennsylvania Gazette turn up linen gowns, jackets, and breeches in a variety of colors.

I have a reprint of "The Art of Dying (sp) : In Two Parts", a reprint of a 1705 translation of a German dyer's manual and a French treatise on dyeing. The colors listed for dyeing linen (pp. 91 - 105) include flesh colored, blue, green (two recipes), yellow (two recipes), black, violet, brown, and purple.

Yes, brown and blue linen show up more often than other colors in the ads, but that doesn't mean the other colors didn't exist, or are incorrect. All too often a "more common/less common" statement becomes an "all/never" statement, and that's just not right. A yellow linen gown or a green linen jacket are perfectly acceptable.

ITEM #19312
March 11, 1756
The Pennsylvania Gazette

NOTICE is hereby given, That JOHN HICKEY continues to carry on the business of dying and linen stamping as usual, in Second street, and purposes to give the publick encouragement by doing any thing that he undertakes, as well as done in Europe, and at as reasonable prices; <snip>
he takes all manner of stains or spots out of silk of cloth, dyes linen or woollen blue, green, red, yellow, purple, or any other colour; dyes and dresses tammies, camblets, poplins or any such like stuff, in the English manner, dyes leather any sort of cloth colour, and has a glaizing engine for chints or calicoes, scowers and renews the colour of scarlet in a particular manner.
------------------------------------

ITEM #76373
January 6, 1790
The Pennsylvania Gazette

Just imported from England, and to be sold, by WILLIAM CRAIG,
At his store in Second street, opposite the Baptist Meeting,

A NEAT assortment of yard wide and 78 Irish linens, and white and brown
Irish sheetings, white Russia sheetings and white Raven's duck, Irish and
Dutch dowlasses, Scotch shirtings, a linen of a strong fabric, oznabrigs,
cotton stripes, white and brown buckrams, brown silesias, Scotch threads,
from No. 7, to 70, coloured ditto, best Baladine sewing silks, scarf twist,
worsted and hair cord for cloaks, mohair buttons, Dunscomb and metal ditto,
silver plated ditto, worsted bindings, shirt buttons, India bandanoe
handkerchiefs, blue and << red linen>> ditto, scarlet serge bobbins, tapes,
silk Marseilles quilting, Joans spinning, moreens, durants, sattinetts,
double and single worsted damasks, calimancoes, crapes, printed 
cottons and callicoes, muslins, fans, red flannels, white ditto, corduroys, ribbons,
cambricks and long lawns, White Chaple needles, pins, spades and shovels,
frying pans, brass kettles, best F.F. gun-powder, plated bridle bitts,
sadlers webb, stirrups, blue plush, tea spoons, silk velvets, mens and
womens beaver pelt gloves and mitts, short pipes, best bohea tea, red lead,
also good upland and meadow hay in a barn near the city. He would let on low
terms, about 10 acres of meadow ground on Greenwich, to any person that
understands raising hemp.

------------------------------------

Letter about cotton and linen dyeing: James Stewart to George Washington, December 28, 1774

London Decr 28th 1774

<snip>
I have also the seed of Wooll and have the thorough knowledge of the
Culture of it and use of it. It is the fundamental die for yellow and
pompadour both in Woolen Cotton & Linnen and yields great profit to the farmer. It is sold in London at 5 sh per Sheaf About the size of a Wheat Sheaf.-- I have also procurred & have packed up 10,000 Plants of Madder in Latin Rubia Tinctorum. I have made myself Master of the Culture & preparing it for the Market and have also all the materials for Manufactoring all the aforemention'd Articles --Madder is the Foundation of all Colours and there are great Quantitites usd of it in London. It is often sold from 10 to 14 pounds per Hundred Wt and
no longer than last year I paid in Virginia 3 Shilling per pound. In
England -- it must be 3 years in the Ground before it can come to perfection now in Turkey its only 2 years therefore am in hopes in Virginia the same.....

I have also sundry Spinning Machines for Spinning of Cotton it spins
25 threads with one person. This machine I have invented myself &
received ye Premium for it of the Society.--I cannot conclude without giving you a more particular Acct. of that Valuable Article of Madder as Madder is an Ingredient so very essential in dying of Cloth & staining of Linnen that neither of them two Manufactorys can be carry'd on without it. It is of the Greatest Consequence to those Branches of Trade to have a Constant supply of
that Valuable commodity & at as low a rate as possible.--
------------------------------------

Posted by Kate Johnson to the 18thCWoman list:

In the cotton/linen section of the Dover book, The Dyer's Companion, by Elijah Bemiss (1806),
starting on p. 57, we find:

3 blue (indigo, blue vitriol)
1 green (logwood/fustic/blue vtiriol) (and one green for silk, dunno why it
was in this chapter!)
1 yellow (onions)
1 orange (copperas)
1 flesh color (black birch and hemlock)
1 red (Nicaragua chips)
1 reddish brown (butternut, sassafras, black alder and hemlock)
1 plumb (logwood, redwood, and verdisgrease, add blue vitriol if needed)
1 purple (logwood)
1 brown (maple or white oak bark)
1 dove on lead (nutgalls and sumac, add logwood and copperas if necessary)
3 olive (nutgalls, copperas, logwood in the first, fustick, logwood and blue
vitriol in the second, the same in the third with a different
proportion/precedure)
1 slate color (copperas , logwood, blue vitriol, different procedure)
2 black (same mixture, with fustick added, for the first, and nutgalls,
copperas, logwood, sumac)

I haven't added in all the mordants and procedures, but it IS interesting to
see...these are for piece goods, I assume, not garment dyeing, though I do
remember seeing ads for re-dyeing clothes to freshen them. I think I'm
going to feel reasonably comfortable making my olive-linen gown, though..

Best--
Kate