steady harbor
While dead, your vision is in black and white, and while you're spectating from death, you can tell what color the shells are when they're first loaded, as obviously the reds are darker than the blues. And it's generally obvious what type of shell was fired depending on if it goes click or boom. However, it's extremely difficult, if not impossible, to tell what shell was ejected when a player drinks beer and the shell is ejected, making it very difficult to keep exact track of what shells are still in the shotgun. Not a big deal to players who just don't spectate, but whenever you're trying to get a feel for your opponents playstyles, tendencies, and skill level, especially when you're eliminated early in the round, it throws a sizeable wrench into your probability calculations.
I suggest having the shells being the only thing that has color in the scene while dead, for clarity, or you could get artsy fartsy with it and make it so only the shotgun and it's shells have color in the scene to make it more striking! "This is the center of your world here, even in death." it says. But if you still want to keep the all black and white, at the very least the shells should flash their color for a second or two, then fade back into black and white at the start and then whenever shells are ejected.