Fire: Almost exclusively Red or Orange.
Water: Almost exclusively Blue.
Air/Wind: Green in most Asian works, yellow otherwise. Sometimes white or a shade of gray.
Earth: Yellow, brown, and orange are all common. Green if nature is not separate or if yellow is already taken.
Ice: In settings where water and ice are distinct, water will tend to be a darker blue, while ice tends toward Lighter Blue like Cyan or even white with a blue tint.
Electricity/Lightning/Thunder: When this element is treated as a separate element (sometimes, it gets lumped with weather), it's pretty much always yellow. In the rare cases it isn't yellow, it will be electric blue, purple or white.
Nature/Plants/Woods: Usually green, perhaps with other earth tones. If dealing specifically with flowers, it will usually be pink.
Metal/Steel: When treated as a distinct element (rather than a subset of earth), metal is usually a metallic gray or silver.
Poison: Green Western Works, Purple in Eastern Works.
Light: Usually White or a bright yellow/gold. Pink, if the power of love is a major aspect.
Holy: Usually pure white.
Darkness: Usually black, though dark purple is also very common. Dark green if it is also centered on poison.
Gravity: Usually purple. Black if associated with black holes or darkness in general.
Magnetism: Usually red for positive charge, and either black, gunmetal gray or blue for negative charge. White for neutral charge.
Energy: Pretty much any color, depending on the type.
Mist/fog/smoke: Usually white if it's fog or mist, gray if it's smoke, and black if it's smog.
Magma/Lava: When treated as a distinct element (rather than a subset of fire), magma/lava is usually orange and very dark gray. Red can also be used as well.
