Colors have traditionally been used in spellcasting to boost the power of a spell. This is specially effective for candle magick. The table I am providing below is by no means an exhaustive list - but simply the meanings that I use. I cannot take credit for coming up with this information - I have gathered it from many different websites:

Color Meanings

Black - Loss, protection from negative spirits, shielding, repel black magic, break hexes, uncrossing. Use in all kinds of banishment rituals - in healing may be used to banish pain and a state of dis-ease. Can also be used to banish bad habits. Use with caution! 

Blue - Harmony in the home and work place, truth, inspiration, wisdom, immortality, loyalty, serenity, sincerity, kindness, patience, fidelity, honesty, devotion. Blue is also the Element color of Water - use in spells involving emotions, healing and mood. 
 
Brown - Earthing energy, concentration, indecision, personal power, communication, balanced color. Use for rituals of materiel increase; eliminates indecisiveness; improves powers of concentration, study, telepathy; increases financial success; locates objects that have been lost.
 
Green - Prosperity, fertility, harmony, health, healing, luck, money, peace, harmony, greed, envy, ambition, success. Stimulates rituals for good luck, money, harmony, and rejuvenation. Green is the elemental color of earth, and can be used to center, protect and ground. Green is a very strong healing color.
 
Magenta - Magenta is the color of the crown chakra and it connects us with the Divine and our spiritual life. Beauty, creativity and inspiration are key words for spells containing this color. Strengthens intuition, imagination, psychic powers, and increases dream activity. Being that Magenta is a combination of 2 colors - red and violet , it oscilates at a high frequency. It energizes rituals where immediate action and high levels of power or spiritual healing are required.
 
Orange - Intellect, friendship, organization, health, self-control, joy, spiritual comfort. Creativity, ability to speak one's mind, ambition, career matters and the Law, self-confidence. Orange is a Solar color can be used in spells invoking the God if needed.

Pink - Affection, love drawing, spiritual awakening, invoking the feminine aspect, unselfishness, leadership. Promotes romance, friendship; standard color for rituals to draw affections; a color of femininity, honor and service. 
 
 Purple/Violet - Ambition, independence, psychic ability, power, progress, protection, honor, pride, royalty, success, idealism, psychic manifestations. This color works well for rituals to secure ambitions, independence, financial rewards, or to make contact with the spiritual other world.

Red - Good health, passion, true love, fertility, strength, courage, will power, sex, anger, aggression, war, strong feeling, pure energy (creative and physical), enthusiasm, warmth, power, sexuality, physical vigor, lust, danger, career goals, fast action, vibrancy, driving force, survival. Protection from fire. Violence. Increases magnetism in rituals; draws Aries and Scorpio energy. Can be very wild and unpredictible (it's either one way or the other). Element Of Fire, Intense in meaning (highly charged). 

White - A balance of all colors; Spiritual enlightenment, cleansing, clairvoyance, healing, truth, sincerity, generosity, expansion and growth, respect. Can also be used in rituals involving lunar energy. White can be substituted for any color candle.

Yellow - Success, creativity, action, development of occult powers, invocation of spirits, inspiration unity. Brings power of concentration and imagination to a ritual. Yellow is ruled by the Element of Air - also may be used in rituals to increase insight, open communication channels and promote wisdom and intelligence.