La corbata roja le queda bien, pero a mí me gusta más la azul.

Quedar bien is a very common Spanish expression for clothes, colours, hairstyles, etc. It means something like:

• to look good on someone
• to suit someone
• sometimes to fit someone well, depending on context

In this sentence, the subject is la corbata roja and the person affected is shown by le.

So the structure is roughly:

• La corbata roja = the red tie
• le = to him / to her / to you (formal)
• queda bien = looks good / suits

Literally, it is closer to The red tie suits him/her than to He looks good in the red tie, although in English both can work depending on context.

Le is an indirect object pronoun meaning:

• to him
• to her
• to you (formal singular, usted)

So without more context, le does not tell you whether the person is male or female. Spanish leaves that ambiguous unless the context makes it clear.

For example:

• La corbata roja le queda bien = The red tie looks good on him/her/you

Because with quedar bien, the person is treated as an indirect object, not a direct object.

Spanish uses:

• me / te / le / nos / os / les
  for indirect objects in this kind of structure.

So:

• La camisa me queda bien = The shirt looks good on me
• Ese color te queda bien = That colour suits you
• La corbata le queda bien = The tie suits him/her

Using lo here would sound wrong.

This is very common in Spanish. The short pronoun me is the one the verb really needs, and a mí is added for:

• emphasis
• contrast
• clarity

In this sentence, a mí is especially natural because the speaker is contrasting their opinion with something else:

• ..., pero a mí me gusta más la azul.
  = ..., but I like the blue one better.

It highlights my opinion.

You could say:

• ..., pero me gusta más la azul.

That is grammatically correct, but a mí gives extra contrast: but as for me...

Because gustar works differently from to like in English.

The basic idea is:

• me gusta X = X is pleasing to me

So in this sentence:

• me gusta más la azul

literally means:

• the blue one pleases me more

That is why:

• me = to me
• gusta = is pleasing
• la azul = the blue one

So Spanish is not saying I like the blue one in the same structure as English; it is using the typical gustar pattern.

Because Spanish often omits a noun when it is already obvious from context.

Here, la corbata has already been mentioned, so la azul means:

• the blue one
• literally, the blue [tie]

The article la shows that the missing noun is feminine singular, because corbata is feminine.

Compare:

• la roja = the red one
• el rojo = the red one (masculine)
• las azules = the blue ones (feminine plural)

This kind of omission is very common and natural in Spanish.

Because adjectives must agree with the noun they describe.

Corbata is:

• feminine
• singular

So the adjectives must also be feminine singular.

That gives:

• roja from rojo
• azul stays azul in the singular

Important detail:

• rojo changes: rojo / roja / rojos / rojas
• azul only changes in the plural: azul / azules

So:

• la corbata roja
• la corbata azul
• las corbatas azules

In Spanish, descriptive adjectives usually come after the noun.

So:

• la corbata roja = the red tie
• el coche azul = the blue car
• la camisa blanca = the white shirt

That is the normal position for colour adjectives.

Sometimes adjectives can go before the noun, but with colours and simple descriptions, the usual order is noun + adjective.

Más means more, and here it expresses preference:

• me gusta más la azul = I like the blue one more
• more natural English: I like the blue one better

It compares the blue tie with the red one that was just mentioned.

So the idea is:

• The red tie suits him/her, but I prefer the blue one.

Spanish often uses más where English might prefer better.

Yes. You could say:

• La corbata roja le queda bien, pero me gusta más la azul.

That is perfectly correct.

Adding a mí makes the contrast stronger:

• ..., pero a mí me gusta más la azul.

It feels a bit like:

• ..., but I personally like the blue one better
• ..., but as for me, I prefer the blue one

So a mí is optional here, but very natural.

Because the subject of gustar here is la azul, which stands for la corbata azul or the blue one. That is singular.

So:

• me gusta la azul = I like the blue one
• me gustan las azules = I like the blue ones

The verb agrees with the thing liked, not with the person who likes it.

That is a key rule with gustar.

It can suggest both, depending on context.

With clothes, quedar bien can mean:

• it looks good on someone
• it suits them
• sometimes it fits them well

In this sentence, because the speaker then compares it with another tie they prefer, the most natural reading is probably:

• The red tie looks good on him/her, but I like the blue one better.

So the focus is mainly on appearance or suitability.

Because pero means but, and it joins two contrasting ideas:

• La corbata roja le queda bien
• pero a mí me gusta más la azul

Spanish punctuation often uses a comma before pero when two full clauses are being contrasted, just as English often does before but.

So the comma is normal and helps mark the contrast clearly.