A black plum is as sweet as a white.

The color of a plum does not reliably tell you how sweet it will taste. What matters is the quality itself, not an assumption drawn from its appearance.

More broadly, the proverb challenges the idea that something is inferior because it looks different from a favored alternative. It urges judgment based on actual qualities rather than surface differences.

Use it to challenge a comparison that favors one option over another solely because of how it looks. The plum image redirects attention from visible differences to the qualities being judged.