The actual diode radiates a single color. White LEDs are red, green & blue LEDs running in parallel. Find a prism & check it out! I have used white LEDs in solid-state amp distortion circuits. For fun, I popped various color LEDs into my transistor tester. The test current is higher than we would see in most pedal diode clipping circuits. These were all 5mm LEDs.
red - 1.58V
yellow - 1.91V
green - 2.72V
blue - 2.67V
violet - 3.03V
white - 2.94V