1. Il a les yeux bruns. (Formal)
2. Il a des yeux bruns. (Informal)
Both translations are correct, but the first is slightly more formal.
The difference lies in the use of "les" (the) and "des" (some). "Les" is used when referring to something specific, while "des" is used when referring to something general.
In this case, "les yeux" refers to the specific eyes of the person being described, while "des yeux" refers to brown eyes in general.