I have a white 2006 Chevy colorado that has a 2” x 4” bell tech lowering kit on it. I’m stepping it up from the stock 15” wheels to black 18” wheels. What size tire would be the best for looks and comfort?
These are the wheels. Black finish. 18”
Tasteful, your suspension setup is what I was imagining for my truck. Although I have 17x8 steel wheels, I am running 235/55r17 which is a little bit shorter than the stock tire. It rides noticeably firmer but overall much nicer than the 215/70r16 wheel/tires that came off. It does look a little small in the wheel well, but I think it would be fine with a lower truck like yours.
Your tires look like they fit the wheel wells nice, so a size with the 18's that have a similar diameter would likely suffice. An online tire size calculator might be a help here.
About the width, I find it is best to slightly "stretch" the tire for the wheel for the best handling. Cramming a too wide tire onto a wheel causes the tire to "roll" sideways in a corner making the steering less predictable/sharp.