Anne-Marie I went with F&B Purbeck stone on kitchen units (I also went for walnut carcas on the inside of the units, I loved the contrast) and F&B railings on the island, it matched in well with the grey slider backdoors. The railings can look dark grey and can also look dark blue/navy at times depending on the light, I love it!
For the walls and ceilings I ended up going with F&B All White as I thought the Purbeck really stood out with it and anything grey might darken it.
I have a tv snug at the other end of the kitchen and I did choose F&B Ammonite for that wall to tie in with the grey tones.
I went for pencil finish on the stone instead but that's just personal choice and I choose SM Quartz Lyskamm as it had more a grey/blue look to the marbling.
Best of luck with your project Lorraine
Q