Meaning of the word "a good horse cannot be of a bad color" in English

What does "a good horse cannot be of a bad color" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

a good horse cannot be of a bad color

US /ə ɡʊd hɔːrs ˈkæn.ɑːt bi əv ə bæd ˈkʌl.ər/
UK /ə ɡʊd hɔːs ˈkæn.ɒt bi əv ə bæd ˈkʌl.ə/
"a good horse cannot be of a bad color" picture

Idiom

the outward appearance of something does not affect its intrinsic value or quality

Example:
The car looks old, but it runs perfectly; after all, a good horse cannot be of a bad color.
Don't judge the book by its cover; a good horse cannot be of a bad color.