The term "FD&C color", often seen on ingredients labels, refers
to "Food, Drug, and Cosmetic" colors. These are organic
compounds (as opposed to inorganic pigments such as
titanium dioxide) that
are so intense in color that very tiny amounts can be used to
color something, and thus can be used in concentrations so
minute that they are safe for consumption.
As further described in the section on
β-carotene, organic dyes
owe their colors to "resonance structures" in the molecule,
where charges are free to move in the molecule at frequencies
that fall in the range of visible light.
There are only seven non-natural (artificial) colors certified for
consumption in the United States:
is allowed only in hotdog and sausage casings.
Other FD&C colors are used in drug coatings and cosmetics.
If one of the above colors is used in a food product, it must
be explicitly labeled in the ingredients list,
(e.g. "contains FD&C Blue #1"). If the label does not
name the compound specifically, but simply says something
like "contains artificial color", then you know it does not
contain one of the colors listed above.
A pigment is a solid that has a color. A dye is a liquid that
has a color. FD&C colors are all dyes. To make a solid color
from a dye, the dye is used to color a solid substance. The
result is called a "lake". One common substrate used is
aluminum hydroxide (commonly used as an antacid). A color made
this way might be labeled "Red 40 Aluminum Lake". Lakes are
often used on the outside of candies and pills, so that the
dye does not wash off, or rub off on fingers.
Besides artificial colors, many natural colors are used in foods.
Some of these are: