Interior house painting: Nice color combos; how to transition between open rooms?

I recently bought a house and I'm looking for painting ideas. First I have the kitchen and dining room as one large room. The dining room also opens up to the living room. There is a 3 sided fireplace and ledge that acts as a separator between living room and dining room. My first question is, does anyone have suggestions on how to divide the kitchen/dining room (vertical molding on the wall, etc) so I could paint 2 different colors? Second, what would be a good 3-color combo for the kitchen, dining room, living room since these rooms all kind of blend?