Absolutely no problem changing up the carpet. Things to watch for......make the transition in a doorway, an opening or along a visual break in the rooms (like the corners of the walls). I would stay in the same colour range, but just go to the other end of the spectrum rather than change the colour completely.....like light grey going to dark grey, not light grey going to navy blue. You want the separation but an easy transition on the eyes.

Love blue tiles. Depending on how much sun and how hot your pool gets in the summer should dictate what color it is. We live in Arizona, so cool blues work best. Our neighbor has brown tile and a dark pebble tech pool. Looks like a swimming hole and gets really hot - 94% water in the summer. They obviously didn't think it through.

Photos would help us a lot but mint and grey usually goes well with charred oak.

I recently saw this episode of Ask This Old House where they demonstrated painting tiles - especially as a solution to get one through till an entire redo is possible. http://www.thisoldhouse.com/toh/tv/ask-toh/video/0,,20902001,00.html Looks like you are doing a great job!