Males have some spots of red, blue, etc. Some can be rather pretty. Native to parts of Central and South America, the native guppy is also called the Millions Fish. This is because it breeds so well. Most guppies stay at about 1-1.5 inches long but they can grow to 2.5 inches.
Guppies do chase each other and other fish but generally do no harm.
They are considered relatively peaceful. They will however eat newly hatched fry of most species. Some other species of fish may nip at fancy guppies' fins. A few gallons per guppy is adequate. They generally live a few years.