Rainbow (1995)

Four kids and a dog embark on the adventure of a lifetime -- the search for the end of the Rainbow. With the aid of computers and an irrepressible belief, they achieve the impossible, finding and riding the multicolored arc. But the gold they take starts a more dangerous adventure, because gold gives the Rainbow energy and the Rainbow gives the world its colors...and if earth loses the color green, no oxygen can be produced. As the world turns black and white, the children battle time and disbelief to restore the Rainbow's power...and save the world.