Why are most glow-in-the-dark things green?
The human eye is most sensitive in green wavelengths. Therefore, if one were to put the same amount of light energy into different wavelengths, the green portion of the spectrum would appear brightest, though it contained no more energy than the rest.

If a phosphor or glow-stick manufacturer is seeking the "greatest bang for the buck", i.e. the most light for the least amount of chemical, green is a good choice.

There is a variety of phosphor colors, such as these listed in Wikipedia:


Red: Yttrium oxide-sulfide activated with europium is a red phosphor used for CRT's.
Yellow: Zinc cadmium sulfide (Zn,Cd)S:Ag, emits yellow light.
Green: Zinc sulfide with copper, ZnS:Cu, emits green light, ~530 nm. It was widely used in CRT oscilloscopes and radar displays because of its long persistence and simple chemistry. It is known as phosphor P31.
Blue: Zinc sulfide with few ppm of silver, ZnS:Ag,emits blue light with peaking at 450 nm. It is known as phosphor P22B and, unlike ZnS:Cu, has a very short persistence, so is suitable for slit-photography CRT's.


For a more complete list of phosphors and their colors, see this useful PDF or Phosphor Technology.

Many stores carry a variety of inexpensive chemiluminescent products, such as glow-in-the-dark necklaces and bracelets, in colors ranging from red through violet.