I see you completely missed the point of my comment in favour of explaining to someone who rather implicitly said it's a non-racist idea, why it's totally not racist.
I suggest you scroll down all of half a dozen comments to the tumblr link specifically demanding white people gtfo and 'let them have their moment'. Absolutely people are saying "white people aren't invited" in not so nice words. That's the only reason this entire event is even remotely controversial.
Racism and discrimination, like sexism and misogyny, are currently used interchangably as and when people feel like it, because one sounds worse than the other. 'racism' is used in the vast majority of cases nowadays to refer to racial discrimination. The Scarman report didn't say "well it's not racism because they don't think blacks are inferior as such." and it's a frankly pathetic point to be trying to hinge on. If only because it's a point you're trying to make in other words to try and devalue the complaint that people are being discriminatory.
Finally, like I quite pointedly stated, #blackout isn't the thing people are having issues with, it's the douchey tumblr people who are trying to behave as social justice doormen by telling white people to fuck off, they're not invited.
To copy your analogy.
Do you understand the distinction now? Group C are being racist/discriminatory. Group A are sat there going "what the hell? what did we do? of course we aren't going to put our smarties in B's bucket, what kind of douche does that?" Group B are getting on with filling up their bucket and admiring their smarties, while Group C is throwing shit and curse words around because it never really liked Group A to begin with.