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.

Black Stones:
General defence, binding, repel dark magick, cursing, reversing
thought-forms and spells into posative power. Saturn rules the color black.
Examples:Jet, obsidian, onyx, hematite, spinel.

Jet:
Is really fosslized stone, black and glassy looking. This is often considered a companion stone to amber and has its static electric properties.
Jet increased psychic awareness but also protects against unwanted dreams and nightmares.
This protection extends to travelling, especially in foreign countries or strange places.

Onyx:
Give protection when you must face adversaries in any kind of circumstanses. This protection goes beyond psyical confrontaion to psychic attack,
or even a subcon. Attack by others or your won sub con. programing. Small balls or flat 'mirrors' of onyx can be used for divination;
these are especially good for past-life work.

Obsidian:
Is formed by volcanic action. The ancient Aztecs used flat mirrors of the stone for divination.
It is grounding and centering stone, protecting you against yourself by making you more balanced.
It is also great for protection. Apache tears are really only small globes of obsidian.

Hemitite:
Is valuble when working to stabilze the life and ground the emotions.

Black Spinel:
Is rather rare. It amplifies psyical and mental energies
during times of stress of crisis. Spinel also draws wealth.