Titanium does not carry a coating. The colour on a tip is an oxide film that grows on the metal itself, thin enough that light reflecting off the top of the film and off the metal beneath interferes. As the film thickens the colour moves through the sequence a fabricator sees at the torch: straw, gold, purple, blue, then a grey-brown.
That last step is the one owners notice. Gold is expected, often wanted. Brown is the point where the film has grown thick and rough enough to stop behaving like a mirror and start behaving like a sponge. It is a change in the film, not in the metal underneath.
A tip runs hot. It sits at the end of the system and holds heat because gas passes over the metal rather than through it. Any titanium surface held in air while hot oxidises, and the film thickens with temperature and time. Gold after long use is the expected result on an unprotected tip.
Brown appears when the film grows past the point where it stays coherent, or when the growth was never even. Brown that arrives in patches, follows the shape of a wipe, or clusters on one side of the tip is not telling you about heat. It is telling you what was on the surface.
Contamination is the first route. Oils, polish residue, fingerprints and road film carbonise into the film as it grows, and the result is a dull grey-brown that will not buff out, because the contamination is inside the oxide rather than on top. Abrasive cleaning is the second: a steel brush or wire wool leaves particles of another metal embedded in the titanium, and those particles rust.
The third is a genuinely overheated surface. A tip run with a restricted outlet, a collapsed baffle or a valve stuck shut sees gas hotter than it should, and the film grows fast and unevenly. That usually starts on the inner lip and works outward, with a leaden, flat look rather than a defined colour band.
Heat is even and directional. It follows the gas path, it is worse inside the tip and around the outlet, and it fades with distance from the source. Contamination is patchy and follows handling: a smudge where a hand went, a streak along the direction of a cloth, a cluster where a cleaning product pooled and dried.
Then compare tip with system. If the muffler and tail section are clean and only the tip is brown, the tip is seeing something the rest of the system is not, and the answer is usually a surface problem. If the colour runs back along the pipe too, look at what the engine is doing.
Wipe a small area with solvent on a white cloth and let it dry. If brown lifts onto the cloth, it was a film sitting on the oxide and the metal underneath is fine. If nothing comes off and the colour is unchanged, the contamination is inside the film, or the film itself is the colour you are seeing.
Run a small magnet over the brown area, then over a clean one. Titanium is not magnetic, so a speck that pulls is embedded steel from a brush or a grinder, and that speck is what will rust first. Also check the outlet for a soot ring or a restriction, because an overheating tip rarely travels alone.
A contaminated or lightly overheated tip can often be brought back. The oxide has to come off mechanically and evenly, without dragging iron into the surface, then be re-polished or left brushed. What cannot be recovered is a film grown into the wall: if the surface feels rough or chalky under a fingernail, the metal has been consumed.
The colour on a titanium exhaust tip records everything that happened to its surface, not only its temperature. Clean handling, cleaning without iron-bearing abrasives and an unrestricted gas path all show in the finish. A titanium exhaust system finished at the tip to the same standard as at the collector holds its colour far longer.
