Yellow, one of the primary colors found in rainbows, is commonly used throughout the world. Traffic lights and signs use it to symbolize caution when traveling. In most cultures, it also represents sunshine, happiness, and warmth. In religions such as Hinduism and ancient Egyptian, yellow is often associated with their deities.
Although not often found in national flags, yellow is prominently used both in the flag of Vatican City (the world's smallest state) and the Holy See (which, although not a country, is the jurisdiction ruled by the pope).
In the 1890s, pencil makers in the United States began coloring their writing implements yellow due to its association with Chinese royalty (China had the best graphite at the time). Today, American pencils retain this tradition.
What few people know is that not only is this color the most visible light of the spectrum, its high reflectance allows it to act as a secondary light source. It is the first wavelength of light processed by the human eye (which belies its use in certain signage and on some emergency rescue vehicles). Our peripheral vision (the ability to see side or fringe areas when we look straight ahead) is 2 1/2 times higher for it than for red.
This pigment also holds the distinction of being the only one that mixes badly with black (producing a rather sick looking pigment).
Appearances of the color yellow
Yellow, in the King James Bible, is recorded four times and is derived from two Hebrew words (Strong's Concordance #H3422, #H6669). Its use lends itself to symbolically representing gold or something of great value (Psalm 68:13), or something leprous or having leprosy (Leviticus 13:30, 32, 36).
This color may be taking over the marketing world. Some recent research reveals that black type against a background colored with it is the best combination for printed material. Tests also show this print combination is the best concerning readability and in the ability of our minds to retain information (memory).
End Time destruction
Revelation 9 discusses the first two of three 'woes' that will come upon mankind during the end time Great Tribulation. The first woe, found in verses 1 to 11, entails humanity tormented for five months (verse 5). The second woe, found in verses 13 to 21, is the unleashing of a huge army that will ultimately kill a third of all humans. This army wears breastplates or armor that look like fire (red or scarlet), jacinth (blue), and brimstone (verse 17). The literal meaning of the Greek word translated 'brimstone' (Strong's #G2306) is 'sulfur' or 'sulfurous,' which is here used to represent yellow.
Brimstone is also used in other parts of Scripture, most notably as one of the two substances (the other being fire) that rained down from heaven to destroy Sodom and Gomorrah. Lot's wife saw, before turning into a pillar of salt, witnessed a downpour of these two destructive forces on the cities and the surrounding region.
A special gift for a King
Frankincense is one of several gifts brought by the Parthian Magi when they came to worship Jesus Christ sometime after his birth. Frankincense, which is yellowish in color, is a dry, rather odorous resin that although grown in Palestine was also imported from Arabia (Jeremiah 6:20, Isaiah 60:6).
Added info on Biblical meaning of yellow
The Bible says the New Jerusalem created by God will have twelve foundations, with each one shining a different kind of light based on a particular precious stone (Revelation 21:19). The seventh foundation (seven is the number of perfection) has Chrysolite within it. The Greek word translated "chrysolite" is a gem that looks like gold or yellow.