Tripe is the stomach of ruminating animals. These animals (i.e., cattle, sheep, goats, etc.) are classified as being four-footed, hooved, cud chewing mammals with a stomach that consists of four chambers.
The protein in tripe is composed of balanced amino acids, each in low concentrations. Some tote this as the ideal food.

This food is a good source of Protein and Zinc, and a very good source of Vitamin B12 and Selenium.

The white tripe that you find in the grocery store has been cleaned, scalded and bleached. It has almost no nutritional value.
Green tripe does not necessarily refer to it's color. Green refers to not having the tripe cleaned, not bleached and not scalded.
It's actual color is brown or black and sometime there will a greenish tint due to the grass or hay the animal ate just before processing.
The spleen is attached to the stomach and is also ground with the tripe.