Rhubarb stalks grow in a spectrum of colors from red to green. In between colors are often called pink or speckled. A deep red petiole is the more popular among consumers, but these plants are often accompanied by poor growth and yield.
Green varieties are often much more productive.
Consumers also often assume the red stemmed rhubarb is sweeter than other colors but color and sweetness are not necessarily related. The Victoria variety, which is probably the greenest variety, can produce some very sweet stems. An Altavista search turned up 100's of web pages mentioning various assorted varieties of rhubarb and some description on its growth, color, popularity and flavor. Below is a summary. Some of the information is contradictory, some is just vague.