ALttP: dark (dark world, mind you)-Not dark at all. It has a dark world, but the atmosphere is always somewhat cheery. There's rarely a moment where one gets the impression that it's dark. graphicwise, no. And there barely even is a story, so no. This game isn't dark at all.
OoT: not very dark- Graphicwise, no. Storywise, somewhat. I mean, you travel forward in time, and the familiar town you arrive in is totally destroyed with zombies in it. It has a few other 'dark' moments, but other than that no, this game isn't really dark
MM: Very dark- Graphicwise, no. Storywise, somewhat. There's a moon that will fall on a kingdom if you never use your ocarina. So what? That isn't any more dark than that one island (Great fish?) getting destroyed in Wind Waker. And that ACTUALLY happened. So, no, this game isn't dark.
WW: not at all- Storywise, this was probably the darkest of them all. AN entire kingdom gets destroyed, multiple people die, an entire island is destroyed, and there really is a hopeless atmosphere to the game until the end. I mean, you're just traveling around this huge sea visiting distant islands wondering if they'll ever connect and a true land will be formed or if the island inhabitants are doomed to slowly die out. Graphicwise, not at all. This game is pretty dark.
TP: Dark-To an extent. It's graphics aren't really that dark except for the Twilight Realm and the tilight sections, but I don't think that warrants for it to be called dark. Storywise, sort of. I mean, it *could* have been the darkest of them all had it been properly worked out. However, it wasn't, so I suppose it's only kind of dark. Overall, it's sort of dark, but not really.
SS: not at -Ok.
I imagine the next game will have 'dark' graphics (Assuming you classify
OoT' and
TP's graphics as 'dark'), and who knows about the storyline? I mean, we've really only been given one dark storyline ever that played up to it's full potential.