Your letter of December 31, 1946 has been received, in which you inquire regarding the situation of a couple whom you describe. As a medical man you know more about tests for colored blood than we know, and if you do not know of any tests that can be made to detect the colored blood, we would assume there has been none yet discovered. People in the South have this problem to meet all the time in a practical way, and we assume that as a practical matter the people there would be able to determine whether or not the sister in question has colored blood. Normally the dark skin and kinky hair would indicate but one thing. As you probably know, the races are badly mixed in Brazil, and no color line is drawn around the mass of the people. The result is, as the reports declare, that a great part of the population of Brazil is colored. The rule of the Church as heretofore followed has been set forth by the early Church leaders. You will find a discussion thereof in Brother Joseph Fielding Smith's book, 'The Way to Perfection,' chapter 16.
[Source: First Presidency, Letter to Francis W. Brown, as quoted in Minutes of the Apostles of The Church of Jesus Christ of Latter-day Saints, 1835-1951, Electronic Edition, 2015]