I think alignment has changed from two axis to one. See diagram below
The first one is a 3.5 style diagram. Each color (blue, purple, red) shows how much far on the law/chaos axis the character is, while the hue (light, normal, dark) shows how good/evil the character is. However, the alignments are rigid: some things are dark purple (neutral evil) and some are dark red (chaotic evil) but each is its own thing.
4e I think is using a shifting scale: in the center is Unaligned (blue), but the farther left you go, the more "good you are" (Good) until you hit the summit: Lawful Good (white). The same is true going right through darkening blue (Evil) and Black (Chaotic Evil). However, there is lots of "wiggle room" for your PC now, doing more evil acts will move you darker and eviler, but doing good things can reverse the trend. (Kinda like Knights of the Old Republic, if you will).
I might be wrong, but that's my theory.