I think you have a great opportunity to use a few different options... A pale color that would be safe for resale like a powder blue or green would be perfect in your kitchen. You could even do a cream color subway tile to add a different neutral color that works with the grey walls and off-white cabinets. If you really like the white subway look, a white marble subway tile would be dreamy! That would keep it white, but would coordinate all the greys, beiges, and off-whites in the room. I think the 3x12 tile is fine, as you're just creating a field of color. However, for the size of your kitchen, a classic 3x6 would be ideal. I hope this helps! I hate to see you taking all your hard work down.

Thank you. I tried to get my kitchen to look like this pic but I think my kitchen is smaller and cabinets are more off white. My perimeter countertop is charcoal and calacutta quartz on peninsula.

Sometimes you start with an idea, then you have to adjust according to where the look is leading. And, there's no problem with that! There are so many good options and it seems like you can't go wrong with the great work you've done so far!