M'agrada el color d'aquesta samarreta, però el que busco és una samarreta blava.

Because agradar works differently from English to like.

In Catalan, agradar is more like to be pleasing to:

• M'agrada el color = The color pleases me
• m' = to me
• agrada = is pleasing

So the person who likes something is not the grammatical subject. The thing liked is the subject.

Because the subject is el color, which is singular.

With agradar, the verb agrees with the thing that is liked, not with the person who likes it.

• M'agrada el color → el color is singular
• M'agraden els colors → els colors is plural

So agrada is correct here because there is only one thing acting as the subject: the color.

Catalan often drops a vowel and uses an apostrophe when two vowels would come together.

Here:

• em agrada → m'agrada
• de aquesta → d'aquesta

This is a normal spelling rule and also reflects the pronunciation.

So:

• m' is the shortened form of em
• d' is the shortened form of de

It means of this T-shirt.

The structure is:

• el color de aquesta samarreta → contracted to el color d'aquesta samarreta

So de shows the relationship between color and T-shirt:

• the color of this T-shirt

In other contexts, de can mean of, from, or other related ideas, but here it is simply of.

Because samarreta is a feminine singular noun.

In Catalan, demonstratives and adjectives agree with the noun in gender and number:

• aquesta = feminine singular this
• blava = feminine singular blue

So:

• aquest llibre = this book
• aquesta samarreta = this T-shirt
• un cotxe blau = a blue car
• una samarreta blava = a blue T-shirt

El que busco means what I’m looking for or the thing I’m looking for.

This is a very common Catalan structure:

• el que = what / the thing that
• busco = I’m looking for

So:

• el que busco és una samarreta blava
  = what I’m looking for is a blue T-shirt

Here, el does not really mean a normal masculine the referring to a specific noun. It is part of the fixed expression el que.

Because Catalan usually leaves out subject pronouns when they are not needed.

The verb ending already tells you who the subject is:

• busco = I look for / I’m looking for

So jo is unnecessary unless you want emphasis or contrast:

• Busco una samarreta blava = normal
• Jo busco una samarreta blava = I’m looking for a blue T-shirt, maybe in contrast with someone else

This is very common in Catalan.

Both are possible in some contexts, but busco is the more natural choice here.

Catalan often uses the simple present where English might use I’m looking for:

• busco = I’m looking for / I look for

Estic buscant is more explicitly progressive and emphasizes the action as happening right now, in the middle of the process.

So:

• el que busco és... sounds very natural
• el que estic buscant és... is possible, but a bit heavier and more emphatic

Because this sentence is identifying or defining something, and Catalan normally uses ser for that.

• el que busco és una samarreta blava = what I’m looking for is a blue T-shirt

Use ser for identity, classification, and essential description.

Use estar more for location or temporary states.

So here you are not describing a temporary condition. You are saying what the thing is.

Because in Catalan, color adjectives normally come after the noun.

• una samarreta blava
• un cotxe vermell
• una casa blanca

This is the standard and most natural order.

Putting the adjective before the noun is usually not normal with basic color descriptions and may sound literary, marked, or simply wrong in everyday speech.

The accent is part of the correct spelling.

Però means but, and the accent shows the stressed open ò sound.

So you should write:

• però

not:

• pero

The accent is not optional.

Because samarreta is a singular countable noun, and Catalan normally uses an article with it here.

• és una samarreta blava = it is a blue T-shirt

You usually cannot just say és samarreta blava in standard Catalan.

So una works just like a in English here.

Not exactly.

• samarreta usually means T-shirt or a casual knit top
• camisa usually means shirt, especially a button-up shirt

So una samarreta blava suggests a blue T-shirt, not a blue dress shirt.

That distinction is useful because English shirt can sometimes be broader than Catalan camisa.