Il colore degli occhi del gatto è interessante.

Italian usually expresses possession with di rather than with an apostrophe-s structure.

So:

• il colore degli occhi del gatto
• literally: the color of the eyes of the cat

This is the normal Italian way to say the cat's eye color or the color of the cat's eyes.

English often stacks nouns or uses apostrophe possession. Italian generally does not do that in the same way.

Both come from di + article contractions.

• degli = di + gli
• del = di + il

So the sentence breaks down like this:

• il colore = the color
• degli occhi = of the eyes
• del gatto = of the cat

Italian very often combines di with the definite article that follows it.

Because occhi is a masculine plural noun beginning with a vowel sound.

The masculine plural definite articles are:

• i for many masculine plural nouns
• gli for masculine plural nouns beginning with a vowel, z, s + consonant, gn, ps, x, etc.

Since occhi begins with a vowel, it takes gli:

• gli occhi = the eyes

Then di + gli becomes degli:

• degli occhi = of the eyes

Because the sentence refers to eyes, plural.

• occhio = eye
• occhi = eyes

So:

• il colore dell'occhio del gatto would mean the color of the cat's eye and would suggest just one eye
• il colore degli occhi del gatto means the color of the cat's eyes

In this sentence, gatto means the cat, a specific cat, not cats in general.

So Italian uses the definite article:

• il gatto = the cat
• del gatto = of the cat

If you said di gatto, it would sound incomplete or would suggest a different kind of meaning, not normal possession here.

Many Italian adjectives do change, but interessante is one of the adjectives that has the same form for masculine and feminine singular.

Here it describes il colore, which is singular masculine:

• il colore è interessante

If the subject were plural, then it would become plural:

• i colori sono interessanti

So interessante stays singular here because colore is singular.

Because this is a sentence with essere:

• Il colore degli occhi del gatto = subject
• è interessante = predicate

After essere, the adjective normally comes after the verb:

• è interessante
• is interesting

This is the most natural word order here.

You could also say:

• È interessante il colore degli occhi del gatto

but that changes the emphasis a little and sounds more marked.

Because è is the verb is from essere.

The accent helps distinguish it from e, which means and.

• è = is
• e = and

So:

• Il colore è interessante = The color is interesting
• Il colore e interessante would be incorrect

Not very naturally.

A word-for-word translation would be:

• The color of the eyes of the cat is interesting

That is understandable, but natural English would usually be:

• The color of the cat's eyes is interesting
• or The cat's eye color is interesting

Italian often uses repeated of the... of the... structures where English prefers apostrophe possession or noun combinations.

Yes.

The full subject is:

• Il colore degli occhi del gatto

The verb is:

• è

And the adjective describing the subject is:

• interessante

So the structure is:

• [subject] + [verb] + [predicate adjective]

Yes, absolutely.

That means:

• The color of my cat's eyes is interesting

Here:

• del mio gatto = of my cat

This is a very common and natural variation if you want to specify whose cat it is.

Italian uses definite articles much more often than English, especially in possession structures.

So where English might say:

• a cat's eyes
• my cat's eyes
• the cat's eyes

Italian often uses a structure with definite articles:

• gli occhi del gatto

This does not sound overly definite in Italian the way a literal English translation might.

A native speaker would understand what you mean, but it is grammatically wrong.

The correct form is:

• degli occhi

because:

• gli occhi is the correct article + noun combination
• di + gli = degli

So you should learn the article first:

• gli occhi

and then the contraction:

• degli occhi

A useful way to learn it is in chunks:

• il colore = the color
• gli occhi = the eyes
• degli occhi = of the eyes
• il gatto = the cat
• del gatto = of the cat
• è interessante = is interesting

This helps because a lot of Italian fluency comes from recognizing common article + noun and preposition + article combinations, not just single words.