Congrats!!
Never ivory or any other shade of white. My husband's cousin wore ivory to our wedding. When they took a family picture(without me!) she looked like the bride. Ask your future daughter-in-law what she would like you to wear. If she has no suggestions ask if she has a sample of bridesmaids dresses. Take the sample and get something that goes with but does not match (don't want to look like a bridsmaid).