I think your original idea makes sense if you want an easy solution. I wouldn't do black, but thats more a gut feeling.
Go with 2 grout colous? One that blends in with the white ones/whatever the obvious choice is, and something that accentuates the pink/maybe even pink grout?
You still have the shape, and it would probably never be exactly the same shade?
Maybe what I am getting at is go even more pastel with the pink tiles (peach maybe?) and stay grey/maybe dark grey with the big ones.
I think your original idea makes sense if you want an easy solution. I wouldn't do black, but thats more a gut feeling.
Go with 2 grout colous? One that blends in with the white ones/whatever the obvious choice is, and something that accentuates the pink/maybe even pink grout?