We're with Valduff. Shades of purple and plum can really add depth to a chic scheme like yours. Particularly with your gorgeous counter top. Grey is also a good call, as it will coordinate with your kitchen units but allow room to add coloured accessories. It can depend on the light quality in your room- we always recommend grabbing some tester opts in a range of shades. Paint your walls or A4 sheets, and see what the colours look like as the light changes throughout the day.

Do you like patterned tiles at all? Doesn’t have to be garish and you can keep the pallet simple. I’m thinking tile the whole wall, the same width as the vanity unit, up to the ceiling, similar to first picture. Or if that’s too much, then just tile the space from the sink to the mirror. I would raise the mirror a little so that it doesn’t get too splashed.

Just something to consider. This is only a digital render but try to consider the colour and warmth or coolness of the upper cupboards against the colour and warmth or coolness of the worktop. If one reads a warmer than the other and they are equal in terms of lightness then they might clash. Cool worktops and off white warm tiles or cupboards are tricky. Additionally, any under counter lighting - get the best you can, with the highest CRI rating. LEDs vary greatly in light quality and temperature.

Are you having wall units? If so you can have the backsplash up to them. If no wall units then 60cm is plenty enough with maybe a taller bit behind the hob. A picture of your kitchen would help us advise better.