How they choose physical characteristics of a baby?

I know in some clinics now they let you choose the gender of the baby and even eye color. they do this through implantation genetic diagnosis. As i understand this chooses the embryo with the characteristics that you want and those are the ones that get implanted.

I was wondering, does this means the baby can just have the same eye color of any of the parents? What happens if you want the baby to have the same eye color of one of the grandmothers..will this be possible?

Also what happens if you want the baby to have an eye color that doesn't run in any of the parents families..can this be achieved? will you need an extra person with those eye characteristics and those can be included in the embryo?

I guess my biggest question is the only method to choose certain characteristics is by excluding the embryos that doesn't have that or you can insert a characteristic in a certain embryo.

Hope you can help me answer this, of course is just for educational purposes. Thanks a lot.