Lá này màu xanh.

Vietnamese often leaves out the equivalent of is/are when describing a quality, color, size, age, etc.

So instead of saying something like Leaf this is green, Vietnamese simply says:

Lá này xanh
or
Lá này màu xanh

This is normal. In fact, adding là here would usually sound wrong in standard Vietnamese.
So Lá này là màu xanh is not the usual way to say it.

No. They are completely different words, and the tone mark changes the meaning.

• lá = leaf
• là = to be / is / are

This is a very important Vietnamese feature: tones are part of the word itself, not just pronunciation detail.

So:

• lá này = this leaf
• là này would not make sense here

In Vietnamese, demonstratives like this and that usually come after the noun.

So:

• lá này = this leaf
• lá đó / lá kia = that leaf

This is one of the biggest word-order differences from English.
English says this leaf. Vietnamese says leaf this.

màu means color.

So màu xanh literally means green color or the color green.

In this sentence, màu makes the color idea explicit. It is a bit like saying:

• This leaf is green
• more literally: This leaf is of green color

Vietnamese often allows both:

• Lá này xanh
• Lá này màu xanh

Both are understandable, but the version with màu focuses more directly on color.

Yes. Lá này xanh is very natural and often more common in everyday speech.

Difference in feeling:

• Lá này xanh = this leaf is green
• Lá này màu xanh = this leaf is green / this leaf is green in color

The sentence with màu can sound a little more explicit, especially if you are talking about colors specifically or contrasting colors.

For example:

• Lá này xanh, lá kia vàng.
  This leaf is green, that leaf is yellow.

Not always. xanh can refer to green or blue, depending on context.

That can surprise English speakers.

Common ways to make it clearer:

• xanh lá cây = green
• xanh dương / xanh da trời = blue

But in a sentence about a leaf, xanh is naturally understood as green, because that fits the context.

So in Lá này màu xanh, nobody is likely to think the leaf is blue unless the situation makes that obvious.

Not necessarily. Lá này is fine.

Vietnamese often uses classifiers, but short everyday sentences can omit them when the meaning is already clear.

You may also hear:

• Chiếc lá này màu xanh.

That is also correct and can sound a little fuller or more specific: this leaf.

For learners, Lá này màu xanh is a perfectly good model sentence.

A rough guide:

• lá: rising tone
• này: low falling tone
• màu: low falling tone
• xanh: level tone

Very roughly for an English speaker:

• lá ≈ la with a rise
• này ≈ nai/nye with a falling tone
• màu ≈ mow with a falling tone
• xanh ≈ sanh (the exact vowel differs by dialect)

Also remember:

• lá and là are not the same
• getting the tone wrong may change the word entirely

Yes, it is correct and natural.

That said, in very casual speech, many speakers might simply say:

Lá này xanh.

The version with màu is still normal, especially when talking about colors more explicitly.

So a good learner takeaway is:

• Lá này xanh = very common, simple
• Lá này màu xanh = also correct, slightly more color-focused

Yes. lá most commonly means leaf, but it can also appear in other meanings related to something thin, flat, or leaf-like, depending on context.

For this sentence, though, it is straightforwardly understood as leaf.

So a learner should mainly remember:

• in isolation here, lá = leaf
• context decides the meaning in other expressions

Yes. This is a very useful pattern.

You can say:

• Hoa này màu đỏ. = This flower is red.
• Áo này màu trắng. = This shirt is white.
• Xe này màu đen. = This car is black.

And often you can also omit màu:

• Hoa này đỏ.
• Áo này trắng.
• Xe này đen.

So the general pattern is:

[noun] + này + màu + [color]
or simply
[noun] + này + [color]

Both are very useful in everyday Vietnamese.