Old movies don't exactly die, but they can literally fade away -- if they were made in color, using one of the less meticulous color processes. In vaults and archives around the world, classic films -- and even some of fairly recent vintage -- are losing their original colorations, dulling down into a vapid blandness that has nothing to do with their original appearance. Filmmaker Martin Scorsese is alarmed about this, and has been pressuring the movie industry to do something about the situation. As part of his campaign, he will visit the New York Film Festival Oct. 5 with The Martin Scorsese Color Show, at which he will show examples of faded footage. Then a complete print of a properly preserved film will be screened: Sergio Leone's epic Once Upon a Time . . . in the West, processed by Technicolor in a three- color-separation imbibition print.