They could always do Pokemon Michael Jackson.
This actually isn't as retarded as you would originally think. Once of MJ's songs was "Doesn't Matter if you're Black or White", or something, I cba to remember the official names of everything. So, you could somewhat make a correlation, but I'm assuming the poster didn't think of that and was trying to make a really bad joke on MJ's skin color. And it's actually pretty fail because he died one year ago yesterday. You could have at least done it at another time so people wouldn't think you are a complete moron. =P
Pokemon Clear also is very viable, since Black and White are the opposite spectrums of the color wheel, and clear is... not a color at all, tbqh. And yes, that would make an Ice-type that much more viable as the third Pokemon, although I don't think it'd matter. You saw the Diamond-Dialga relationship with a shared bluish color, and the Pearl-Palkia relationship with the shared pinkish color. But Platinum and Giratina? They don't really share colors, tbqh.
Red/Blue/Yellow(/Green) were all colors.
Gold/Silver were colors or metals, Crystal is a crystal.
Ruby/Sapphire/Emerald are all precious gemstones.
Diamond/Pearl were precious gems, Platinum is a metal.
So, only the first two games are guaranteed to have some sort of correlation, and we already see that with Black-White, two ends of the color spectrum. But the third game doesn't have to be a color as Gen I was, or doesn't have to be the same (a color, really) as Gen III games were. I hope that it is either Gray or Clear, but just pointing out that Gens II and IV didn't have any sort of linkage between the three games.
EDIT: Poison isn't a defensive nor offensive type. For offense, it only gets super-effective coverage on Grass, it has four resistances and one
extremely common immunity, that being Steel. It also doesn't get very good offensive moves (although that is subject to change) outside of Cross Poison or something. Toxic gets wide distribution so I don't even consider that a Poison-type move.
On defense, it takes damage from Ground-type attacks, and only has Grass, Fighting, Bug and Poison resistances. Grass is not very seen, Fighting and Bug let it counter Heracross, but not really anything else, and the only thing good about a Poison resistance is that it gets Toxic immunity. DDRMaster, in the previous post, stated Dark/Poison. I liked the type at first, but you lose the key Fighting and Bug resistances you had before with mono-Poison. So you can't really switch into Megahorns or Close Combats/Dynamicpunches without having a bunch of HP and DEF EVs.
And we have Water/Dark in the form of Sharpedo(phile), but I wouldn't mind a faster, not-so-frail one for OU.