You're still free to theorize their existence in the can. The blue and green ones too. But I'm going to point out that there's no evidence for red, blue, or green marbles in the can. So you'll probably call me a white marble alarmist, even though I concede the existence of black marbles in the can.
>> I concede the existence of black marbles in the can.
So it’s a concession, how white of you...
Well, the red marbles were hiding for fear of being attacked by ignorant school children.
Which reminds me, two pretzels were walking down the road...