Purple-in-grain is a dark red color. Before the advent of modern chemistry, all coloring agents came from natural sources, and this particular color was produced from grinding up the bodies of an insect species. The color was described as “in-grain” because the tiny insect bodies look like seeds or grains.

It took forty thousand insects to produce just one pound of this dye, and it was highly prized because it didn't fade. Eventually, the phrase “in-grain” came to refer to any dye that was long-lasting. This led to our modern word “engrained” to describe any object or mental attitude which is fixed or enduring.