Green about the gills

Gills, of course, are the organs through which fish breathe, but from the early 1600s gills also described the flesh under the jaws and ears of humans. To look green about the gills means to look ill and dates from 1628. According to the OED, it joins a number of expressions that describe how people can look ill, dejected or well - ‘green, yellow, blue, white, rosy etc’ around the gills.