89k km on my IS350. I replaced the spark plugs today and took the photo of the old spark plugs. I assume these tell me the engine is running fine, but I also notice that the left three plugs (passenger side) look much darker than the right three (driver side)
Is there anything I should worry about? thank you.

 

Look into the spark plug tubes on the passenger side and see if you see any oil residue. You might have three bad tube seals on your valve cover there. They're minor, but something to monitor. My passenger side rear-most tube seal is passing a tiny bit of oil right now.