You say you were planing on placing the ceramic border on a 45 degree angle? ( diagonal )
Here is a tip. For a better look you will install the 45 degree angle border tiles first. And then the rest of the tile.. Make sure you get a straight line off of the outside wall and all the other line going off of that. I.E. the interior walls will not be exactly 90 degrees from the outsidewall. (no home is)
as far as the color difference. A contrast is always better.
Good luck with the project.
let me know if you have any problems.