You know, I always thought I was shooting really dirty ammo when I shot a stainless 1911, then I changed to one in black Armor-tuff and noticed the black gun didn't get as dirty using the same ammo and was much easier to clean. .... it all came down to appearance.
Tighter guns don't get dirtier unless you mean to suggest dirt it more easily blown free from 'loose' guns, such as out through the rails, around through the exterior area of the muzzle during recoil (such as on tilt barrel guns like Glocks or Kahrs), down the mag well, etc., which doesn't seem to actually happen to any great extent, tight or otherwise.