A colon is a punctuation mark used to precede a list, quotation or description within a sentence. It is adds a pause to spoken English which is intermediate in length between a comma and a period. Generally, the fragment that precedes the colon is a complete sentence. The portion of the sentence after the colon is often an aside and does not need to be a complete sentence. A colon is also used to separate the speaker from the dialogue in a play. Mathematically, it indicates ratios and has several computer programming functions. It is also used to separate minutes from hours in time and to separate chapter from verse in quotations from the Bible.
This will be a short row. I had two navy blues, two browns and one black to use. Here they are sewn together.