Red~
Health, Vitality, Power, Passion Courage, Sex, Protection,
Defensive Magick, Love, Friendships, Creativity, This is a very powerful color to work with.
(according to some books it's also good for Aries and Scorpio energy). Relates to the element of fire, the planets mars,
jupiter,and the sun, and is the color of the zodiac signs Aries, Leo, and Saggitarius. (not coincidentaly, considering those are the fire signs,
and their ruled by the sun, mars, and jupiter. In fact, I think that same little 'rule' is the same with all the other signs).

Orange~
This is a color used mostly for the attraction of things, like energy, ambition, confidance, pretty much motivation.
I'v read in a few books that this color should not be used to much.
That you should only use it when it's neccasary, and not to use more than you have to.
But other books give no such warning.
I think it's pretty much just a judgment call on the part of you and how it reacts to your own body chemistry.

Green~
Wealth, Prosperity, peace, Balance, Earth spells, Growth, Faeries, Luck,
Success, Healing, (according to some books it's good for Cancer and Saggitarius energy).

Blue~
Creativity, Tranquility, Truth, Wisdom, Protection, Astral Projection,
Healing, Happiness, Psychic Mind, Peace, Meditation, Patience, understanding, Spirituality,
(Saggitarius, Pisces, and Aquarius energy).

Black~
Absorption (Negative), Protection, Banishment, (and I'v read that for a balance of the energies
you should put a black candle on the left of your altar, and a white candle on the right.

White~
Clairvoyance, Truth, Meditation, Peace, Spiritual Strength,
Lunar Energy, Astral Travel, Purity, Protection, an all-around handy candle,
good if you can't use a certain color.
But the right color for the right purpose is always suggested. :)

Pink~
Friendships, Love/Romance, Morality, Peace, Compassion,
Relaxation, Luck, (Libra energy).

Purple~
Compassion, Understanding, Independance, Emotions, Healing, Power,
Success, Psychic Development, Creativity, (Gemini energy).

We'v reached these conclusions with the aid of 7 books:
Making Magick by Edain Mccoy,
Faery Wicca by Kisma K. Stephanich,
Everyday Wicca by Gerina Dunwich,
Earth, Air, Fire, Water by Scott Cunningham,
Earth Power by Scott Cunningham,
In the Circle by Elen Hawke,
Buckland's Complete guide to witchcraft by Raymond Buckland,
And I did a few double-checks with several books by Silver Ravenwolf.