My name is Jason and I am the administrator and starter of this site. I am a mixed-race person and just about 90% of all my living relatives are, too. The church has put out guidelines that state that it is recommended to marry within your own "culture" for the sole reason that mixing cultures has shown to be hard on marriages (this is true both inside the church and out). 
 
It has nothing to do with race. 
 
For instance, an american, full-caucasian (white) girl that was born and raised in the Phillipines (let's say because she was from a military family) could marry a local Phillipino and have a very successful marriage. This is because she was raised in the same country and understands the culture.  
 
However, a white girl from Utah could have significantly more marital problems marrying the same Philipino guy. 
 
I come from a culture where it is common to take in family members to live with you if they are struggling or need help, or to give them money without the expectation of getting paid back. Many Americans, no matter what race they are, have had problems marrying into my culture. 
 
What it all boils down to is that your marriage will be successful if: 
 
1. You learn to sacrifice for your spouse. 
2. You make the Gospel of Jesus Christ your culture, leaving all other cultural practices and expectations behind it.