Why the colors matter
Seoul's city buses are color-coded by route type, and the color tells you what kind of trip that bus is built for before you even check the number. This matters more here than in most cities because Seoul runs thousands of routes across four categories, and the color is the fastest way to tell them apart at a glance from across the street.
Blue buses (trunk routes) run the longest distances, connecting major districts across the city along main roads — these are the backbone routes, and the blue is meant to evoke the Han River and Seoul's skyline.
Green buses (branch routes) cover shorter distances, typically feeding people from neighborhoods into the nearest subway station or a blue-bus trunk line. They're operated somewhat more flexibly by private companies and are the ones you'll ride most if you're going somewhere a subway line doesn't quite reach — the green is meant to evoke the mountains ringing the city.
Red buses (express routes) connect Seoul to satellite cities in the surrounding Gyeonggi-do province — places like Incheon, Suwon, or Bundang — running express with fewer stops over longer distances. If you're staying in Seoul proper, you'll mostly encounter these at bus terminals rather than city-center stops.
Yellow buses (circular routes) loop through central and sub-central business districts, connecting things like city hall areas, shopping districts, and major stations in a circuit rather than a straight line. There are far fewer yellow routes than the other three colors, and where they exist, they're aimed squarely at short hops within a compact downtown loop.
Each bus route also carries a number, and the first digit generally tells you which district it starts from, which is useful once you're trying to distinguish between two similarly-colored buses at a stop.
Fares and transfers
City buses use the same T-money card (or compatible transit card / phone) as the subway — nothing new to buy if you're already using one for the metro. A standard city bus ride costs ₩1,500 with a transit card (cash costs more and won't get you transfer discounts, so tap a card if you have one).
The transfer discount is the part worth understanding: if you tap out of a bus or subway and tap into another bus or subway within a set window — normally 30 minutes, extended to about 60 minutes late at night — the fare system treats it as a continuation of the same trip rather than a new fare, up to several transfers. That only works with a card, and only if you remember to tap your card again when you get off the bus, not just when you board — skip that tap-out and you lose the discount on your next ride, even though the bus itself doesn't require it to let you off.
Double-decker and premium express buses (usually the longer-distance red routes) can cost more than the standard fare — check the posted fare on the bus door or in a transit app before boarding if the route looks like a long-haul one.
Night buses: the Owl Bus
Seoul's subway and most regular city buses stop running around midnight to 1am, which is exactly when the city's nightlife is often just getting going. The Owl Bus (올빼미버스, sometimes called the night bus or 심야버스) fills that gap: a network of routes that only run late at night, easy to spot because each one carries a route number starting with N (for "night"), plus an owl logo on the bus itself.
Owl Buses generally run from around midnight to 5am, spaced roughly 30–50 minutes apart depending on the route — noticeably less frequent than daytime service, so it's worth checking a transit app for the next departure rather than just showing up and waiting. Routes are designed using anonymized late-night phone and taxi data to follow where people actually travel after dark, which is how the network ended up threading through nightlife districts like Hongdae, Gangnam, Jongno, and Dongdaemun rather than just mirroring daytime bus lines.
For a tourist, the practical use case is simple: if you're out past the last subway train and don't want to pay for a taxi across the city, check whether an N-route runs near where you are and where you're headed. It uses the same T-money card as every other bus, so there's no separate ticket to buy — just a matter of knowing the network exists and roughly which letter to look for on the display.