TT, if they do add a new Type, then the chance of it being "Light Type" is practically zero. Not to mention Light types dont always beat Dark types (Im not talking about actual Pokemon types; just monster types in General).
Anyways, colour is important as they give us an idea about 2 more Next Generation Mons, and Matthew, you do have a point about Diamond and Pearls, and how they are created... Maybe the two Legendarys can create these gems, and the teams after them want to become rich?
Bah... Who knows... Maybe they're both made out of these materials (Like the Regis), and hell, if a Pokemon can withstand such enormous pressure, they must be practically invulnerable to attacks right? Thats probably my best wild theory of why Teams would be after them, but who knows? In the GSC era, neither Lugia or Ho oh were being persued, although Suicune was, in Crystal...
And Trevor, yes, these are the next sets of games.