From poetry to music to movies, we’re always hearing about the “deep blue sea.” But the seas aren’t always deep blue. And sometimes, they’re not blue at all. They can be green, brown, or other colors. And each color can tell us something about what’s happening in that part of the sea.

Understanding what the colors are telling us is one goal of PACE—Plankton, Aerosol, Cloud, Ocean Ecosystem—a NASA satellite that launched in February.

[3, 2, 1, booster ignition ... Full-power engines and liftoff of the Falcon 9 and PACE—helping keep pace with our ever-changing ocean and atmosphere...]

The mission is studying how the oceans and atmosphere interact, tracking their health, charting marine resources, and more. And ocean color plays a big role in all of that.

The water can be tinted by tiny organisms known as phytoplankton. Some of them turn the water green—a result of the chlorophyll they use to convert sunlight to energy. Plankton attract fish and other large animals. So keeping an eye on the color can help scientists track the health of fisheries.

Massive blooms of some types of algae, on the other hand, can stain the water brown or red. They may use up much of the oxygen in the water, turning a region into a “dead zone” where not many other organisms can live. They can also produce toxins that make shellfish dangerous to eat. So tracking the blooms—by looking for their colors from space—can help keep people safe.