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.

Red stones:
Use for energy, courage, defence, pshyical love, sexuality, strength, power. As the color of blood, it symbolizes birth, death, and rebirth.
Red is ruled by mars. Examples: Garnet, ruby, red jasper, ed agate, dark carnelians, flurite, rhodochrosite, light rhodonite, chaledony, beryl.

Garrnets:
Paticulerly the deep purpleish-red ones, are wonderful for sources of extra energy. They are mars and fire.
Ruby: Promotes succes in buisness and money projects, protection from all enemies and spirits, and an increase in energies during rituals.

Red jasper:
A gem of mars and fire, is an excellant protective stone.
It can defend the magicion by sending negativity back to the sender.
Red Agate: Also known as blood agate, is a Fire stone. It promotes atmospheres of peace and calm.

Dark Carnelian:
Is a gem of sun and fire. It is worn to gain courage and self confidance. It counteracts negative thought and defends you against others who are trying to read your mind.

Red Fluorite:
Helps you to get your thoughts in order and free yourself from emotional decisions and attachments that may be hindering you.

Rhodocrosite:
Although usually a pink color, can sometimes be found in a deeper shade nearing red tints. It draws energy without stress.

Rhodonite:
Comes in many tints and intesities of red. It helps to get rid of doubts, but also helps to shut down the psychic centers. This particulerly helps if you are being bombarded by the virbrations of others.

Chalcedony:
Creates energy and succes in lawsuites.

Beryl:
Can strangthen the attraction between lovers or simply attract love.