First choose one color for all the walls if after you move in you want to change a wall color do it yourself. Most builders will only paint one color anyway. Where does the need for the blue come from? You will need a backsplash unless the counter material is already going to be the 4” piece above the counter. If you want help post pics of the choices up till now. Blues are bverydifficult to work with BTW and I would stay from blue based grays unless you have sepcific pieces that you can show us that are in the blue family.So alittle more info from you before even beginning to suggest color for walls. Dallas white can have many different colors in it so take pictures of your slabs you have chosen and post those for sure. Do not let the builder choose your slabs