Symbolism
Okay, this isn't going to be extremely long, but it will cover two things. These are two questions my brothers asked me about Yu-Gi-Oh! and Digimon, so I thought maybe other people wondered to. The first concerns the colors red and green, the second concerns light and dark.
Red and Green:
In the opening of the first season of Yu-Gi-Oh! (English dubbed) there is a shot of Yami and Pegasus, Yami is surrounded by a red 'aura' and Pegasus by a green one. Now, that seemed odd to my brothers, but it actually makes perfect sense. Let me tell you why.
In America the color red generally represents the bad guy. Maybe it is because it is the color of blood, or of anger, who knows. And green represents good guys. That could be because it is the color of growing things, or the color the army wears. Again, I don't really know. I'm all for blaming it on George Lucas and Star Wars. Luke's lightsaber was green, Darth Vader's was red. Green = good, red = bad. See?
Anyway, in eastern cultures (such as Japan), however, red represents royalty, nobility, and honor. They painted their palaces that color, royalty wore red clothing, etc. So, anyone in red is probably going to be in some sort of honorable or heroic position. (That's why the lead Power Ranger was almost always red, the leader in Digimon generally likes red, fire people are important, etc.)
So, basically in anime red=good, green=ummm... well, if not always bad, at least not as good as red.
Light and Dark:
Okay, so this has to do with both Yu-Gi-Oh! and Digimon season 4. Basically my brothers were wondering how Yami (who's very name means darkness, and who is obsessed with Dark Magic cards and dark clothing) can be good. They also wondered about that whole "true darkness" thing concerning Kouichi.
Batman aside, in western cultures we tend to view light=good, and dark=bad. I think it is probably based upon the biblical references to those living in sin as living in darkness, and lovers of Christ being light to the world. However, we seem to miss other references where God created light and dark together, God came over the land as darkness, etc. But that's beside the point. The point is, we teach our children to be afraid of the dark, we refer to evil people as having black hearts, and our novelists will say "there was something dark and evil about him."
In eastern cultures dark can be bad also. However, so can light. When these two things are being used for evil they are seen as corrupted light and dark. But "true" light and darkness remain good even if someone evil is using the corrupt form. True darkness can overcome corrupted darkness as easily as light can. And true darkness is needed (generally working in conjunction with light) to defeat evil. (That's why I think Yami and Seto end up working together to save the world. Light and Darkness, but anyway, that's another issue). This is seen with Koji and Kouichi in Digimon Frontier (season 4), with the Light and Dark cards in CCS, etc. I think I can best sum up the Japanese view of light and dark in one line.
"As true light reveals the depths of a darkened cavern, so true darkness reveals the depths of a man's character."
That's my quote, so don't steal it ~_^