Il pigmento lascia un'impronta blu.

Because pigmento begins with a normal consonant sound (p), so it takes the regular masculine singular article il.

• il pigmento = the pigment

You use lo before certain special consonant sounds, such as:

• lo studente
• lo zaino
• lo psicologo

So pigmento does not need lo.

Lascia is the third person singular form of the verb lasciare, which usually means to leave, to let, or in this context to leave behind / produce.

So:

• lasciare = to leave
• lascia = he/she/it leaves

In this sentence, the subject is il pigmento, which is singular, so the verb must also be singular:

• Il pigmento lascia ... = The pigment leaves ...

The apostrophe appears because una becomes un' before a feminine singular noun that begins with a vowel.

• una impronta → un'impronta

This is called elision.

Since impronta is feminine and starts with i, Italian shortens una to un'.

Compare:

• una macchia = a stain
• un'impronta = an imprint

Be careful: this un' is feminine here. It is different from masculine un.

A good clue is the ending -a, which is very often feminine in Italian.

So:

• l'impronta
• un'impronta

are feminine forms.

Also, the article confirms it:

• un' before a vowel here comes from una, not from masculine un

So the sentence is using a feminine noun: impronta.

Yes. In Italian, adjectives often come after the noun.

So:

• un'impronta blu = a blue imprint

This is very normal Italian word order.

English usually says:

• a blue imprint

But Italian commonly says:

• noun + adjective

Some adjectives can also come before the noun in Italian, but color adjectives like blu are very commonly placed after it.

No. Blu is one of those Italian color adjectives that is invariable, meaning it does not change form.

So you can say:

• un'impronta blu
• impronte blu
• un cielo blu
• occhi blu

The word blu stays the same.

This is different from many other adjectives, which do change:

• rosso / rossa / rossi / rosse

But blu remains blu.

Because blu is an adjective, not a noun here.

The article belongs to the noun:

• un'impronta = an imprint

Then blu describes that noun:

• un'impronta blu = a blue imprint

So the structure is:

• article + noun + adjective

There is no need for a separate article before the adjective.

Yes. In Italian, lasciare is very commonly used to mean to leave a trace, mark, stain, impression, or sign.

For example:

• lasciare una traccia = to leave a trace
• lasciare un segno = to leave a mark
• lasciare una macchia = to leave a stain

So il pigmento lascia un'impronta blu sounds natural: the pigment leaves a blue imprint.

A helpful approximation is:

• oo-NEEM-PRON-ta

A few details:

• un' is pronounced smoothly into the next word
• impronta has the stress on pron
• the r is an Italian r, usually tapped or lightly rolled

So the phrase un'impronta should sound connected, not broken apart.

In standard Italian, the preferred form is un'impronta blu.

While una impronta may be understandable, it is not the normal standard written form. Before a feminine singular noun beginning with a vowel, Italian usually uses elision:

• una amica → un'amica
• una impronta → un'impronta

So you should learn un'impronta as the correct standard form.

The structure is:

• Il pigmento = subject
• lascia = verb
• un'impronta blu = direct object

So it follows a straightforward pattern:

• Subject + Verb + Object

Word by word:

• Il = the
• pigmento = pigment
• lascia = leaves
• un'impronta = an imprint
• blu = blue

This is a very typical Italian sentence pattern.