Translation:The best milk is perfectly white.
Is 가장 좋은 commonly used? I thought the word for best is 최고
최고 (and all the other 최 words) are chinese-based. 가장 좋은 is korean.
I even thought 제일
The meaning isn't obvious in this sentence. This sentence could also mean "The milk I like the most/my favorite milk is..."
But in that case the answer would not be white, but brown ;-)