Translation:The four walls have different colors.
If anybody is wondering what is the difference between "la parete" and "il muro" :
- They are used interchangeably most of the time.
- In short "la parete" would be a wall in a closed space (internal wall), while "il muro" can refer to a wall built anywhere (il Muro di Berlino).
- "la parete" is used in biology, while "muro" isn't. (the cell walls = le pareti cellulari)
To the best of my knowledge, "to be" is a linking verb, which means it can have an adjective in an object, and it links it to the subject. "To have" does not have this property, so the adjective must be used together with a noun it modifies. E.g.: "She is kind" but "She has a kind character". I am not a native English speaker, however, so I might be wrong.