Latin
An ad hoc version contributed by Jasper Griffin via Julia Griffin and Jürgen Gutsch:
Si virtus tenera floret pulcherrima forma
iste niger non est: candidus, ecce, gener.
If the power of the most beautiful blooms in a tender form
This son-in-law is not black: [he’s] white, look.
An ad hoc version by Prof. Dr. Wilfried Stroh (Munich University) via Jürgen Gutsch:
Si pulchra una bonis virtus probitasque videtur,
pulchrior hercle magis quam niger iste gener.
Back-translation by Jürgen Gutsch:
If real virtue and honesty count as beautiful for good people,
Then, indeed, your son-in-law is far more beautiful (= white/fair) than black (=ugly).