Gemstones Colors

When we say "color" we are often talking about hue. It is the component of color we talk about most. It indicates whether a color looks red, green, blue, yellow, orange, etc.

As an example, look below at the line of different hues. Notice how they look like colors from a rainbow.

Color Hues

Hue values range between 0 and 360 degrees. They take on these values because they are placed around a circle. 

The Number of Colors

The National Bureau of Standards (US) lists 267 color names. Berlin & Kay (1969) studied color terms in 100 languages and proposed that there exist 11 universal color terms: white, black, red, green, yellow, blue, brown, purple, pink, orange, gray. This result was confirmed experimentally in American observers by Boynton & Olson (1987), and in both Japanese and American observers by Uchikawa & Boynton (1987). The number of discriminable colors probably exceeds 10,000. Not all discriminable differences are separated into different color categories (names). 

Saturation represents how pure a color is. As an example of saturation, think about rubies color increasing the saturation will change the color from:

deep red -> vivid red -> intense red -> red -> pinkish-red. 

Saturation 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%
Brightness tells us how strong a color is. For example, the sun has a high brightness, while a birthday candle has a low brightness. Colors like whites and yellows have a high brightness. Colors like browns and grays have a medium brightness. Colors like black have a low brightness. 
[Sample Brightnesses]
As an example, here are several bluish squares. As you go from left to right they increase in brightness. 
Blue Brightness Bar
When we talked about hue we said that hue values are between 0 and 360 degrees because they are frequently laid out around a circle.

If we lay them out around a circle and also increase the saturation as we move away from the center, we get the circle shown below. The hue changes as we go around the circle, and the colors also get more saturated as you move towards the edge of the circle. In the center they are very faded; near the outside of the
circle they are very pure. If you change
Color Circlethe circle to a cylinder, along the axes of the cylinder, the change in brightness can be shown 
Additive Color Mixture:below are two demonstrations of additive color mixture. In the figure on the left the primaries are red, green and blue.  Where they all overlap (the bulging triangular region in the center) they combine to produce white. The demonstration on the left illustrates that any three primary lights (in this case a cyan, a purple and an orange) can similarly be used to produce white.