Когда тушь заканчивается, ресницы уже не выглядят такими тёмными, и приходится красить брови аккуратнее.

Here тушь means mascara.

But yes, тушь can also mean ink in other contexts, especially drawing ink or writing ink. Russian often relies on context to tell you which meaning is intended.

A useful grammar note: тушь is a feminine noun even though it ends in ь. That is very common with nouns of this type.

In this sentence, заканчиваться means to come to an end or to run out.

The non-reflexive verb заканчивать is usually transitive:

• заканчивать книгу = to finish a book
• заканчивать работу = to finish work

The reflexive/intransitive заканчиваться is used when the thing itself is ending:

• урок заканчивается = the lesson is ending
• деньги заканчиваются = the money is running out
• тушь заканчивается = the mascara is running out

So here -ся does not mean oneself. It helps form the intransitive verb meaning to end / run out.

Заканчивается is imperfective present, and here it gives a general, recurring meaning:

• Когда тушь заканчивается... = When mascara starts running out / whenever the mascara is getting low...

It sounds like a typical situation, not one single future event.

If you said Когда тушь закончится..., that would more naturally mean When the mascara runs out completely in a specific future instance.

So the difference is roughly:

• заканчивается = a repeated or ongoing situation
• закончится = one completed future event

Уже не usually means no longer or not anymore.

So:

• ресницы уже не выглядят... = the eyelashes no longer look...

Literally it is already not, but in natural English the best translation is usually no longer.

After выглядеть meaning to look / appear, Russian often uses the instrumental case for the quality or appearance being described.

Compare:

• она выглядит уставшей = she looks tired
• он выглядит странным = he looks strange
• ресницы выглядят тёмными = the eyelashes look dark

Since ресницы is plural, the adjective must also be plural:

• тёмными = instrumental plural of тёмный
• такими = instrumental plural of такой

So the structure is normal Russian grammar:

• выглядеть + instrumental
• выглядят такими тёмными = look that/so/as dark

Такими comes from такой and here it means something like:

• that
• so
• as

In this sentence, because of the negative не, the most natural English idea is:

• не выглядят такими тёмными = do not look as dark
• or do not look that dark anymore

So такими points to the degree of darkness, not just the basic quality dark.

Приходится is a very common impersonal Russian construction meaning:

• to have to
• to be forced to
• it becomes necessary to

The person can be stated in the dative:

• мне приходится = I have to
• тебе приходится = you have to
• нам приходится = we have to

But Russian often leaves that person out when it is obvious from context or meant in a general sense.

So here:

• и приходится красить брови аккуратнее

means something like:

• and you/I/one have to do the eyebrows more carefully

The exact subject is understood from context rather than explicitly stated.

After приходится, Russian often uses the imperfective infinitive when the meaning is repeated, habitual, or focused on the activity itself rather than on one completed result.

So:

• приходится красить брови аккуратнее = one has to color/do the eyebrows more carefully

This sounds like a recurring necessity whenever the mascara gets low.

If you used a perfective infinitive such as покрасить, it would sound more like one specific completed action:

• приходится покрасить... = have to color them once, get it done

The imperfective красить fits better here because the sentence describes a typical situation.

In beauty and cosmetics language, красить is broader than literal English paint.

Красить брови can mean:

• to color the eyebrows
• to tint the eyebrows
• to fill in the eyebrows
• to do the eyebrows with makeup

So in this context it does not necessarily mean permanent dyeing. It simply means applying color to make the eyebrows look right.

Russian uses красить very naturally for makeup-related actions:

• красить ресницы = do/apply mascara to the eyelashes
• красить губы = put color/lipstick on the lips
• красить брови = do/fill in the eyebrows

Here аккуратнее is functioning as an adverb, modifying красить.

It means:

• more carefully
• more neatly

So:

• красить брови аккуратнее = to do/color the eyebrows more carefully

Formally, аккуратнее is the comparative form, related to аккуратно or аккуратный.

Russian very often uses this simple comparative form instead of a longer expression with более:

• аккуратнее = more carefully
• быстрее = faster
• точнее = more precisely

So the idea is that, once the mascara is running out, extra care is needed with the eyebrows.