The color gray is recorded nine times in the KJV Bible, with all its occurrences appearing in the Old Testament. The Hebrew seybah (Strong's #H7872), used 19 times, is translated "gray hairs" (or head) in Genesis 42:38, 44:29, 31, Deuteronomy 32:25, Proverbs 20:29 and Hosea 7:9. It is additionally the basis for the single word "grayheaded" in 1Samuel 12:2, Job 15:10 and Psalm 71:18.
The remaining occurrences of seybah are translated into synonymous phrases such as "old age" (Genesis 15:15), "hoary head" (Leviticus 19:32), "hoar head" (1Kings 2:6), "hoary" (Job 41:32), and "hoar hairs" (Isaiah 46:4). A hoary (hoar) headed individual is one who possesses locks that are gray in color.
A person with a hoary head has reached an advanced age that deserves to be respected (Leviticus 19:32). This look many times means a level of wisdom has been achieved through experience, although this is not always the case.
I said, 'The aged should speak, and the multitude of years should teach wisdom.' . . . Great men are not always wise; neither do the aged understand justice (Job 32:7, 9, HBFV, see also Ecclesiastes 4:13).
The gray (hoary) head is a crown of glory if it is found in the way of righteousness (Proverbs 16:31, HBFV).
Why does it change?
Hair color is created and maintained by the pigment melanin which is injected into each follicle by specialized cells. At a certain age (which varies from person to person), however, the amount of melanin injected decreases and eventually stops. Hairs without this pigment eventually turns gray and then white.
Appearances of the color gray
Job's questioning of God's wisdom, and his complaint that what happened to him was unfair (Job 38:2), received a personal response from the Lord. Part of the verbal correction he received entailed asking him if he could catch the mighty marine-based animal called a Leviathan (41:1). The beast could move so fast that it left an unusually colored wake.
He leaves a shining wake behind him; one would think the deep had gray hair! (Job 41:32, HCSB).
Agates, composed of silica, are one of several precious gemstones used in the High Priest's breatplate (Exodus 28:19, 39:12). It can be colorless or have several bands of this pigment as well as white or red.
Other precious gemstones that can possess this coloration are Chalcedony stones. Their name is derived from the ancient city of Chalcedon where they were believed to be first discovered. It is one of the gemstones God will use to adorn one of New Jerusalem's twelve foundations (Revelation 21:19). Other common colors found within these gems include variations of white, brown, green and blue.
Added info on meaning of gray
An idiom is an expression whose meaning cannot be determined by the literal interpretation of the words. Three English idioms related to this color are the following.
A "gray area" is a concept or topic that is not clearly defined or that exists somewhere between two extreme positions. People who are referred to as "gray suits" are those who are in business, politics or government who, though unknown, make important decisions behind the scenes.
A "gray market" is one that operates between one that is legal (white market) and one that is illegal (black market). These markets sell products which are legal to own but which are illegal to fully use or can be used illegally.