I have just had the same dilemma re waterline tiles and I realised two things (if it helps)... Firstly it's the colour of the coping that I needed to match to, or compliment, the tile. And secondly, the colour of the tile matters if your pool is fully tiled, but if you are going with pebblecrete, then it's the colour of the pebblecrete that affects the colour of the pool and not the tile! First time pool builder, so who knew?! My fingers did do a lot of googling to decide on pebblecrete colours though. Good luck!

We used concrete look tiles in our bathrooms, and decided on the same tile (outdoor version) for our pool area. We also used it for our pool coping and waterline tile and edge of the steps. The tiler cut the tiles, and we had a guy come onsite to hone the edges (same effect as the ones in your photo, but same tile on coping and waterline) who did a wonderful job and really reasonable price. This may not be what you are after, but we did not want any glitzy tiles. Photos below

Barnes.... I actually know of a product that cleans that off with ease!!! It's new has had testing and has been through the process of intellectual property and is now currently under production. If you are interested I can try source you some.

I quite like the idea of using same tiles as you have around edge of pool. Here are some pics to help visualise how it might look. The last one has almost charcoal coloured tiles, which would look pretty good as contrast to your lighter tiles and the blue waterline mosaics.