Believe it or not, the custom of the Tallit stripes are an outgrowth of the Torah command to attach one blue thread to the Tzitzit, and also used for dying priestly garments. (see Exodus 25:4 and Numbers 15:38) The "Techelet" was a bluish color, obtained from the fluid of a sea creature called the "Chilazon." (Tosefta Menachot 9:6) It is found on the coast of Northern Israel, though here is a disagreement among scholars regarding what the "chilazon" actually is. Some say that it is a snail, while others say it is a squid. There are some who claim that the "chilazon" is actually a mollusk. At any rate, this particular dye was very precious and because of its value, the Romans (who conquered Israel in 63 BCE) seized control of its usage. This caused the Jewish dyers to go underground. By 639 CE at the time of the Arab conquest, the secret of Techelet was lost all together. As a commermoration of the blue thread, blue stripes were added to the Tallit itself. These later morphed into black stripes. So while there is an origin to this custom, there is no halachic legal requirement to have any stripes on the Tallit, and if someone does choose to have stripes, they can be of any color(s). However, keep in mind that the current custom of black stripes is keeping within the synagogue decorum, which has value in and of itself. http://judaism.about.com/library/3_askrabbi_o/bl_simmons_tallit.htm

There are a number of reasons: 1) To remind us of the "techailet", a dark greenish-blue dye that was used on one of four strings on each corner of the Talit (Numbers 15:38). This dye was produced by a sea creature, but nowadays most Jewish authorities believe that we don't know which creature it is, so rather not dye any of the strings. So, the stripes would remind us of that dye. That's why you'll see that some people have blue stripes on their Talit, not black. The others, who use black stripes, would rather not imply that they are using techailet on their Talit today. 2) According to Kabbalah, white represents Divine Benevolence and the dark stripe represents G-d’s strictness. Accordingly, the Talit is mainly white, with a few streaks of black, showing that G-d is primarily kind. 3) And simply, one wears a Talit in the morning, when one says the Shema prayer. The earliest time to say that prayer is when it is light enough to distinguish between white and "techailet" With its "stripe" design, the Talit reminds us when the earliest time to use it is.

Before you are admitted into Heaven, Gd scans your Tallit bar code. *Beep* "OK, You may enter". :)