The color of stones is really just as important as what kind of stone it is. And when you pick a stone, as with any magick, it is important to know how this perticular stone, not the kind, but the individual stone, reacts to your own body chemistry, your feeling about the stone is always more important then the kind, or color. And make sure before buying your stones that you know that what you are thinking your buying, really is what it says it is. Alot of stores sell these magickal semi-precious stones.
Or you could just find stones in nature, preferably in a magickal spot you feel power.
Then, once you buy or find your stones, you must cleanse them. Sometimes they don't need cleansing when you find them in nature, but it's better to be absolutely sure that you don't get any negative energies mixed in with you magick. Or even if the other energies aren't negative, it's best to be sure that when you charge a stone, that's all it's charged with, it works best that way, and you can be sure that your magick is done purely.
I'v read many different methods for cleansing, so whatever has worked for you before, or what you trust will work, or whatever you'v read is best for whatever certain thing your planning to use your stone for, you should do.

Green Stones:
Growth, fertility, money, marraige, good health, grounding and balancing. Green is ruled by venus. Examples: Jade, malachite, amozonite, emerald, aventrurine, nephrite, tourmaline, olivine, green quartz, chrysoprase, fluorite

Jade:
Comes in many colors wich can be used under their color catigory. Green jade is particulerly powerful for money and any type of growth in the field of buisness and sucess.
It is a venus water stone

Malachite:
A tranquil blue/green stone, has bands of varius bands of green and hite hues through it.
As a venus/earth gem, it protects its owner in both love and sbusness succsess. be careful with your emotions when using this stone, it absorbs both pos. andd neg. energies.

Amazonite:
A stone of uranus and earth, it helps when gambling. gambling here meaning venture, wether it be buisness, relationg shops, shcooling or whatever.

Emeralds:
Are one of theose most expensive stones there is. as a venus and earth gem, it is valuble in magick. if it's too much money ofr you, you can use a sub. the emeralds power is through making others aware of your talent, your buisness, or your owrth in a field. It atracts mental wisdon, and helps correlate it with spiritual wisdom.

Aventurine:
is a mercury and air stone. it attract money through perception, cretivtiy, an dintteligance.

Nephrite:
is closely related to jade, adn is a lovely green color. as an earth stone, it boths draws and preseves wealth.

Chrysoprase:
venus and earth sotne. it is a lucky stone wich attracts sucess in any new ventures adn better money condistoins.

Tourmaline:
comes in many colors, but he green shades, of venus and earth, attract money and buisness success, and stimulate creativiyt. be cautious, because its ability to energize and can create emotional and mental havoc if the user is not properly balanced on all levals of being.

Olivine:
is a volcanic green stone of volcanic orgin. good luck, luve and money are attracted by this stone. it also protectsf from theives.

Green quartz:
stimulates creativity, increses money, generaly attracts an easier life through good fortune.