Can I assume you are not blipping the throttle as you let the bike warm up? Knowing you just added a 'can to the bike......... seems likely you want to hear the music.
As it's probably still pretty cold out in PA..... the FZ's FI will be running open loop in 'rich' mode, to simulate a choke until the engine warms up. More fuel in the mixture means you are likely to see some of it in the exhaust. Especially with the new after market can. It's probably not doing anything different than it was before you added the can; but now you can see it.
4000 miles on a 4 year old bike is not a lot of miles. Almost too low, by my view. The bike would have to have sat for a majority of it's life so far without running. Sitting still is not the best thing for a motor.
I agree you probably have rings that aren't sealing really well..... not so bad as to cause you major issues; just not as good as they could be. High RPM on a cold motor would show you this more.... revving the motor when it's cold would put extra oil into the exhaust, and you'd see that more with the engine cold because the catalytic converter is not hot enough to burn it off. The after market cans are obviously much less restrictive, so more of that oil is getting out the end of the pipes.
If you want to know for sure how good the rings and valves are sealing, you need to do a compression test to verify you are getting the seal you need, on all four cylinders. The shop manual will tell you how many pounds of pressure the cylinders should be able to make, and also tell you how much variation between cylinders is acceptable.
If your numbers are in the 'good' range........ let the bike warm all the way up before you beat on it. It's possible you just have some left over fuel and stuff in the pipe, and nothing at all is wrong. All FZ6s will make more fumes and smoke until the cat gets warmed up, and the rings expand, and the head warms up.
