I agree that it can be upsetting at this stage but your timber will all darken naturally and the difference will become less obvious over time and once you have furniture and rugs in place it's likely to be one of those issues that only you and no one else will notice. And I defy anyone to not have something like this in their house which has been newly built/renovated. I know this isn't terribly helpful but I don't think ripping anything up to start again or going to great lengths to seek recompense from supplier/installer is going to help your blood pressure either (by all means raise concerns with them and ask for suggestions from them).

You don't match your walls to your floor but to your taste. What colours do you like? The nice thing about timber flooring is that it's neutral. It goes with everything.

Do your undercoat in vivid white. Then add 2 top coats in one area in one colour and the other colour in another section. I would have thought the warmer natural white would be better tonally, But what are you trying to achieveL

At first I thought OMG what are you thinking with putting a grey kitchen in with all that beautiful wood. But I did a google search, and found the colours look good together. I would keep the floor a neutral colour and pattern. Not concrete look, not wood look, definitely not slate look. Refer to the photo below, a neutral floor with the grey kitchen, let the wood be the feature.