(1) apparent color is the color of a water sample that has not had particulates filtered out;

(2) true color is the color of a water sample that has had all particulates filtered out.

The measurement of true color is the one most commonly used by scientists. To measure true color, the color of the filtered water sample is matched to one from a spectrum of standard colors. Each of the standard colors has been assigned a number on a scale of platinum-cobalt units (abbreviated as either PCU or Pt-Co units). On the PCU scale, a higher value of true color represents water that is darker in color.

THE ROLE OF COLOR IN WATERBODIES
More than 75% of Florida's waterbodies have color values less than 70 PCU. Waterbodies in the LAKEWATCH database have average color values ranging from 0 to over 700 PCU.

Dissolved organic materials such as humic acids from decaying leaves, and dissolved minerals can give water a reddish brown "tea" color.

The presence of color can reduce both the quantity and quality of light penetrating into the water column. Changing the quantity and quality of light reaching the bottom of a waterbody can influence the depth of colonization and the types of aquatic plants and algae that can grow there. In some waterbodies, color is the limiting environmental factor. For example, high color concentrations (greater than 50 PCU) may limit both the quantity and types of algae growing in a waterbody.

Waterbodies that adjoin poorly drained areas (such as swamps) often have darker water, especially after a rainfall. Consequently, the location of a waterbody has a strong influence on its color. For example, lakes in the well-drained New Hope Ridge/Greenhead Slope lake region in northwestern Florida (in Washington, Bay, Calhoun, and Jackson Counties) tend to have color values below 10 PCU; while lakes in the poorly-drained Okefenokee Plains lake region in north Florida (in Baker, Columbia, and Hamilton Counties) tend to have values above 100 PCU.

HEALTH CONCERNS:
There is no known direct health hazard of water color. Consequently, an acceptable level of color depends on personal preference. Water transparency, however, may be reduced in highly colored waters (greater than 50 PCU) to the point where underwater hazards may be concealed, creating a potentially dangerous situation for swimmers, skiers, and boaters.