There is nothing wrong with parents preferring specific traits over another as long as they are not motivated by prejudice against other people with different traits. If there is not any coercion or influence from society, the preference of a parent about what their child should look like is not unethical.
This is comparable to potential parents that decide to become pregnant via sperm donor. A sperm donor is typically asked to submit photos of themselves throughout their life, medical history, a voice recording, and other personal information to help inform the potential parent think about what their child would be like.
If parents are able to pick and choose certain features in a sperm donor, it is ethical for parents to have the ability to alter a child they have conceived.