Worntorn,
Only the Combat could produce colored smoke; it is a function of the tank/side cover colors.
Mine, obviously, produces the sought-after yellow smoke at WOT, but only when the smoke selector switch is on. This is done by turning the key one more click beyond ignition/lights position (again, ONLY the Combat had this special switch feature).
From time to time one might see a red tank/sidecover Combat, switch in correct position, emitting red smoke, but the yellow is by far the most dramatic.
I myself have seen quite a few black Combats spewing black smoke - even at idle. Some have, over the years, tried to attribute the Combat smoke-production to insufficiently-robust bearings, unable to contain the awesome Combat power. But us Combat owners know the truth.
The Combat's ability to produce colored smoke, available only in 1972, was of course what the Japanese were after when they began flooding the market with two-stroke bikes. They were successful to a point, in that they could produce smoke - but only grayish-white in color. An unexpected bonus was that they picked up a lot of power in the process, which is why you still see two-strokes - even though they sound funny. I will never forget my first encounter with a Z-1; it is painful to admit, but he was faster than me! But my smoke was prettier, so there.
Sadly, very few of us are left that can make colored smoke, as the special switches fail over time, no originals have been available for many years, and the technology to make an after-market version has been lost in the mists of time.