As an infant, my daughter would stare at white-on-white designs more than any other. I agree with the quilter who mentioned that many toys are made in black and white designs to meet an infant's developmental level. Add this to the beautiful new gray, black and white contemporary prints and you have my suggestion to go for the parent's request. (I think it is very touching that they are taking into consideration the sister's feelings at this special time.) If a contrasting color is needed for the other side, I feel that bright yellow or mid-range bright green would be nice with white/grey/black & pepto-pink.