There are a variety of Shotokan Karate belts. Developed by the Funakoshis (Gichin and Gigo), Shotokan Karate is a distinct type of martial art that is known for its fluidity, grappling, and katas. Since its inception in 1924, Shotokan Karate has gained both notoriety and respect within the various arts of fighting.
Shotokan Karate belts are based off of their original branch. Hence, the influence of mainline Karate is well evident in many aspects of Shotokan. Karate uses several sets of color-coordinated belts to refer to its numerous ranks. As an offspring of Karate, Shotokan Karate also (for the most part) uses a lot of different colors for its ranks. As with any other martial art, there are variations within Shotokan Karate that may utilize different ranking systems.
Karate belts use the kyu/dan system. Kyu belts, mostly known as those Shotokan Karate belts which are beneath black, come in very different colors. From white to brown, the student usually progresses through the Kyu system by obtaining darker colors as time goes on (i.e. white to yellow, yellow to orange, etc.). Once the pupil becomes a black belt, he/she moves on into the Dan system of Karate belts. Under the Dan rankings, every black belt has the same color: black, albeit with different stripes (often commonly referred to as "degrees").
Students begin with white belts. In Shotokan Karate, all students (unless unexamined), begin with a white-colored belt. Traditionally, this white belt later turned darker, browner, and eventually black with sweat. Many opponents of the Kyu system prefer schools that do not award different colored belts until achievement of the most senior rank ("black").
Students end with some type of black belt. Because the degrees to black belts are so specialized in Shotokan Karate, it's hard to nail down all of the Dan systems. Nonetheless, most continue the set layed down by Gichin that progressed from white to brown to black. Colors in between are optional for schools within Shotokan Karate.
Aside from the highest and lowest degrees, Shotokan Karate belts are optional within schools. That being said, most take cues from mainline Karate and implement the Kyu/Dan ranks to properly identify skill/experience. Good luck, grasshopper, and may the Shotokan guide your way.