rather a mild brown color not like rust but like a waxy residue.
It's two parts,,Rust
AND wax build up from the Wonderlube.
The
HOT water used during your cleaning does lead too "flash rust". Switch to luke warm/tepid temp soapy water for cleaning and the flash rust will not occur. I also run some 90% Isopropyl or Denatured Alchohol in the bore after washing and drying the bore. The alchohol will mix with any remaining water and assist evaperation,,just pour some in, slosh it around and pour it out,,you can even pour it back in the jug and use it again.
Then I lube the bore with a good gun oil,,
ALWAYS carefull to remove the oil before shooting the next time. I usta use the bore butter an wonderlube stuff,,got tired of the left over gunk and build up in the bores,, accuracy was falling off too,,