To some this up for people not wanting to look through tables: in basically every metric you could possibly imagine, mix-raced children are worse off. They have (as compared to their constituent races):
Substantially lower GPA's and IQ's
Worse general health
Substance abuse issues are often doubled or tripled in race-mixed children
Increased suicidal thoughts and tendencies
Repeating school grades
Much higher risk of migraines or perpetual headaches
And to top it off they do not look like their parents.

All of that is from just that one study. I remember multiple studies that describe the many skin issues that race-mixed children are much more prone to including eczema and cystic acne. I believe, again, from what I remember, that a good MAJORITY of mixed-race children will either experience eczema or cystic acne at some point in their lives.

To be fair, though, much the same could be said of two people of the same race who differ significantly in physical appearance.  Case in point, the daughters of Bruce Willis and Demi Moore.  Both of them are very attractive people, but the daughters, sadly, are nowhere near as attractive as either of their parents.

Is there a troll in our midst?  If so, he’s of “mixed race” and confused.  Among Catholics, one’s faith is the distinction, not race.  While it’s true that most people prefer someone of the same race and culture for a marriage partner, there are always exceptions.  I’m acquainted with several fine Catholic families whose parents are different races.  In one case, a Filipino man married to a Caucasian American woman.  They have 15 children.  Another is a mixed race, Black/White woman married to a very dark gentleman from the Caribbean.  They have 11 natural children and one adopted child who is Cambodian.  There are no children with genetic defects from the parents.  The Cambodian child has rare genetic mental and intellectual challenges, as a result of her birth parents’ exposure to napalm during the Vietnam War.  The parents gave her up to the care of an orphanage because of their poverty and lack of education. 
The Church has no policy on race mixing except that its prohibition is morally wrong.
Depending upon the prevalent culture where a Catholic couple of mixed race live, the only concern has more to do with sociology and prudence than religion. In some places, mixed rave couples are seen as acceptable.  No big issue exists.  In other places, being of mixed race can create social issues which the couple and their children have to deal with.  If they’re okay with this, there’s no genetic barrier.