Color plays an important role in magick-making, and witches generally have an array of colored candles to use for different spells:

WHITE

purity, peace

RED

sexual energy, strength, courage

PINK

love, friendship

BLUE

healing, truth, inspiration, higher wisdom

GREEN

abundance, fertility, good luck, harmony, money

YELLOW

creative imagination, communication

PURPLE

spiritual power, psychic ability

ORANGE/GOLD

positive thinking, justice

SILVER

channeling, clairvoyance, astral energies