Follow...what? I remember saying this a long time ago, but I still can't agree with it definitely being Grey. R/S's third game would have been amethyst in that case, a combination of a red gem and a blue gem. Platinum is a metal where neither of the ones before were metals. Red and Blue don't make Yellow. Gold and Silver don't make Crystal. Why do people think that "Black and White makes Grey" is a solid argument for Pokemon?
The only argument I can think of towards that would be the Kyurem being grey argument, but what if they named it Pokemon Crimson like they trademarked and use Volcarona...I could also see a Brown, or something that's not even color-related.
Just to be a pain in the ass but, there is actually a logic when thinking
RBY series. :D All those three colours are primary colours that you can't get by mixing other colours together. You can only get something alike but not clear and pure red, blue or yellow.
As for
the second generation, we have to dig a little deeper from the source we'd not expect to provide any logic for those names. From the Bible. Basicly, gold is thought to mean good of love and knowledge of celestial things. While silver is to mean truth of wisdom and knowledge of spiritual things.
And to find harmony between those two paths we need to clear our mind so it is as clear as a crystal. :D Get it?
The third generation has, well, more modest idea. All three of them are gemstones but through ages ruby and sapphire has been thought to have some sort of connection. As if they were each others opposites.
But the real connection is that each of them, ruby, sapphire and emerald, has been thought to have a power or etc. For example, ruby was thought to have power to predict the future of it's owner by its coloration. Henry VIII's first wife was said to have predicted her own demise by the darkening of a ruby ring. Sapphire was said to darken in color if worn by a person who had committed adultery. While emerald can lose it's coloration if heated to extreme temperatures. :P
Also, emerald is thought to increase emotions of sympathy, love and a sense of fairness and justice.
SORRY for getting of topic, personally I believe that the third game if it is to come and would be tied with Black and White might have the name of Turquoise or something alike.