Color is the aspect of things that is caused by differing qualities of light being reflected or emitted by them. To see color, you have to have light. When light shines on an object some colors bounce off the object and others are absorbed by it. Our eyes only see the colors that are bounced off or reflected. The sun’s rays contain all the colors of the rainbow mixed together. This mixture is known as white light. When white light strikes a white crayon or marker barrel, it appears white to us because it absorbs no color and reflects all color equally. A black crayon or marker cap absorbs all colors equally and reflects none, so it looks black to us. While artists consider black a color, scientists do not because black is the absence of all color.
A book is a medium for recording information in the form of writing and images, typically composed of pages that are bound together and protected by a cover. The technical term for this physical arrangement is codex. A single sheet in a codex is a leaf, and each side of a leaf is a page. In the history of hand-held physical supports for extended written compositions or records, the scroll dominated the written world prior to the codex.
Postal codes are strings of numbers (and sometimes letters) that help postal services determine where a piece of mail is being sent to. They help simplify the task of bringing post to its destination. Nations throughout the world use postal codes, and though the systems and formats vary, the common trait is that they all make the postman's job a little easier. These codes indicate the extent of delivery jurisdictions. Every delivery point that falls under the same jurisdiction is one whole postal code, and anything beyond those dividing lines are counted as a different code. Sometimes postal codes are tied to geographical areas or administrative boundaries. Sometimes they're more free-floating. In some cases, they are attached to a specific organization, or even to a single delivery point. In all cases, they are closely tied to and heavily defined by where the postal employee goes when delivering the mail.