That is a hard one with those tiles. I would have to think if you did a white, it would kind of work with the colour of your tiles. At the end of the day, they do need to be replaces, but as you said, due to budgeting reasons, you cannot, I can pass on this photo of a nice bathroom with those tiles for you though for inspiration... : )

Schots have heritage style pencil tiles in black, dark green and burgundy https://www.schots.com.au/tiles-parquetry/ceramic-tiles.html#q=&idx=schots_production_default_products&p=0&hFR[categories.level0][0]=Tiles%20%26%20Parquetry%20%2F%2F%2F%20Ceramic%20Tiles%20%2F%2F%2F%20Bullnose%20%26%20Pencil%20Borders&nR[visibility_catalog][=][0]=1&is_v=1. Blue might be tricker to find.

Sounds like a very stressful situation! If there is absolutely no way the builder will allow you to change things (even if they did, I imagine they would ask you to foot the entire bill of pulling the tiles down and replacing all water proofing in addition to new tiles), I can make a few suggestions for improvement. Firstly I would suggest replacing the tiles above the vanity with a white mosaic, a patterned or a textured feature tile/strip. You could also use this same tile to replace the vertical feature in the shower. There are some beautiful shapes and sizes available to choose from. Secondly I would address the grout situation in this way: Floor - dark colour grout & Walls - Light colour grout. Lastly if it does not prove too difficult or expensive, maybe replace the tiles below the vanity with a plain white tile (could be similar size). Good luck and I am sure once you have a lovely mirror up and some crisp white towels, it will look just wonderful.

Tile selection can have a big impact on the cost of your bathroom reno. The cost of the tiles per sqm is one thing, but did you know that most tilers charge different rates for the "Type" of tile laid large format and or vitrified tiles will cost more to install These are a few hard and fast rules we give our clients when they are selecting tiles for a bathroom renovation 1 - opt for darker tiles and darker grout for the floor - as a wet area light coloured tiles on the ground are harder to keep clean 2 - If you are opting for a feature tile - let it be the hero. That means make the rest of the tiles plain - large format subway tiles give you enough texture without detracting from the feature 3 - always opt for square tiles on the ground - trying to get the correct falls using rectangular tiles will mean you will have extra cuts and the floor will look a mess. The second reason we opt for square format for the floor is because of subway tiles You see, back when everyone was opting for square tiles on walls, it was easy to install square on the floor and get all the grout lines to match. Now most people are opting for subway tiles, you can never get all the grout lines to match, therefore installing square means you dont have to match grout lines as they are different format. If you are installing your subway tiles vertically, then there is a chance you will still be able to get all grout lines to match if you have selected the same sized square format tile hope this makes sense I have added a link to a blog that explains more about tile selection