red and dead

The phrase red and dead is used in astronomy to describe galaxies with no (or minimal) star formation or early stars. "Dead" in the sense of not producing stars, and "red" being the color of long-lasting stars. Non-red stars are brighter and shorter-living, becoming rare as time passes if star formation has fallen off. A typical red and dead galaxy is elliptical.

The term blue and new has also been used (though not as often), for galaxies at the opposite extreme: showing a blue color from a substantial number of short-life stars.