Sight unseen, when this "open floor plan nonsense fad" is over you will have a lot of company. Why anyone would want view of the kitchen from everywhere in the house is a mystery to me. I here all the excuses and theories, but don't buy any of them. Your separation idea with color is right. Make sure the colors look good together, then simply follow function. Walls that serve the kitchen paint one color and change for the living area when. I think what is bothering you is changing colors on a flat wall that serves one part kitchen and one part living room. I have seen people put up moldings to try to explain the change and that looks tacky. What I do that looks fabulous is to find a fancy stripe wallpaper. What I mean by fancy stripe is a stripe that in itself ihas a pattern. I Have used ones that have a greek key for example. Anyway find the fancy stripe wallpaper stripe that will look good against each color, cut out the stripes (about 1" to 2" wide and use them as a border wherever the color ischanged. Go to my site ganttsdecorating.com and look through the pictures and the blog on decorating walls and you will see what I mean. Sorry for being so long winded. Good luck let me know if this helped. Bill