What produces those color smoke trails behind fighter jets?

Question

When these jets perform what is used to produce those amazing colored smoke trails? If you don't know that i mean here's a picture ..

http://www.airliners.net/photo/UK---Air/British-Aerospace-Hawk/1376095/L/

Answer 1

Smoke generator.  Here's a link to describe:

http://www.sandersaircraft.com/generator...

Answer 2

These are produced by smoke canisters usually mounted on the wings, tailplane and fuselage and triggered from the cockpit.

Answer 3

Dyed diesel fuel.  

Answer 4

One way is food coloring in water.