No m'agrada el blau; jo prefereixo el vermell.

Because agradar works differently from English to like.

In Catalan, agradar literally works more like to be pleasing to. So:

• M'agrada el blau = Blue is pleasing to me
• literally: To me, the blue pleases

That is why the verb agrees with el blau (the thing liked), not with me.

• el blau is singular, so you get agrada
• if it were plural, you would say M'agraden els llibres = I like books

M' is a shortened form of em, the unstressed pronoun meaning to me.

So:

• em agrada becomes m'agrada before a vowel

This contraction is very common in Catalan:

• m'agrada
• t'agrada
• l'agrada

It happens for smoother pronunciation.

Here, blau and vermell are being used as nouns, meaning the color blue and the color red, not as adjectives.

So:

• el blau = blue / the color blue
• el vermell = red / the color red

Catalan normally uses the article in this kind of structure.

Compare:

• M'agrada el blau = I like blue
• El cotxe blau = the blue car

In the second example, blau is an adjective describing cotxe.

In this sentence, they are functioning as nouns.

That is why they appear with the article:

• el blau
• el vermell

But these same words can also be adjectives:

• una camisa blava = a blue shirt
• un cotxe vermell = a red car

So the word class depends on how the word is being used in the sentence.

Yes. Catalan often omits subject pronouns because the verb ending already tells you who the subject is.

So you could simply say:

• No m'agrada el blau; prefereixo el vermell.

That would be completely natural.

Here, jo is included for emphasis or contrast. It highlights the speaker's personal preference:

• No m'agrada el blau; jo prefereixo el vermell.
• roughly: I don't like blue; I prefer red.

So jo is not required, but it adds emphasis.

That is the normal way to form negation in Catalan.

• M'agrada el blau = I like blue
• No m'agrada el blau = I don't like blue

So no goes directly before the verb phrase.

This is similar to Spanish and different from English, which uses do not.

Yes, preferir is irregular in the present tense.

The form prefereixo means I prefer.

The verb changes in the stem, so it does not behave like a fully regular -ir verb. Some present-tense forms are:

• jo prefereixo
• tu prefereixes
• ell/ella prefereix
• nosaltres preferim
• vosaltres preferiu
• ells/elles prefereixen

So prefereixo is the correct I form.

Yes, often you can.

Catalan commonly uses estimar més to mean to prefer in everyday speech:

• M'estimo més el vermell = I prefer red

That said, prefereixo is also perfectly correct and clear. Depending on the region or style, one may sound more common than the other.

So:

• prefereixo = standard and direct
• m'estimo més = also very natural, often conversational

Yes. The semicolon is just a punctuation choice.

You could also write:

• No m'agrada el blau. Jo prefereixo el vermell.
• No m'agrada el blau, jo prefereixo el vermell.

The semicolon helps link two closely related statements while still keeping them clearly separate. It is a stylistic choice, not a grammar requirement.

Yes. That is also correct, but the emphasis changes slightly.

Compare:

• No m'agrada el blau = neutral, standard
• El blau no m'agrada = emphasizes blue

The second version sounds a bit more like:

• As for blue, I don't like it
• or Blue, I don't like

So both are grammatical; the difference is mainly one of focus.

Because when Catalan refers to a color as a noun, it normally uses the article.

So:

• prefereixo el vermell = I prefer red
• literally: I prefer the red

English often leaves the article out in this kind of sentence, but Catalan usually does not.

No. Vermell is a standard and very common word for red, but in some varieties of Catalan, especially Valencian, you may also hear roig.

So depending on the dialect, both can exist:

• vermell
• roig

In this sentence, vermell is completely standard and natural.

You would simply remove no:

• M'agrada el blau; jo prefereixo el vermell.

That means:

• I like blue; I prefer red.

So the only change needed is the negative particle:

• No m'agrada = I don't like
• M'agrada = I like