i'm using leds, fiber optics+leds and bulbs on my schratchs ...
for the fiber, i'm making a "light box" with aluminium cheets inside (from my kitchen). and i'm making as many wholes as colors needed .. then i'm using professional color filter (not affected by heat) beneath the light and the fiber. you can also directly paint the end of the fiber with a transparent color (i'm using humbrol for exemple)