ما بحب اللون الاحمر كتير، بس اختي بتحبه وبدها قميص احمر.

ما is the negation word here.
So:

• بحب = I like
• ما بحب = I don’t like

This is a very common way to negate present-tense verbs in Levantine Arabic.

In Levantine, بـ usually marks the normal present or habitual tense.

• بحب = I like / I love
• بتحب = you like or she likes, depending on context
• بتحبه = she likes it

So the b- is one of the things that makes the verb sound colloquial/Levantine rather than Modern Standard Arabic.

كتير means a lot, much, or very, depending on context.
In this sentence, ما بحب اللون الاحمر كتير means I don’t like the color red very much.

With verbs, كتير often means a lot / much.
With adjectives, it often means very.

Here, بس means but:

• ما بحب اللون الاحمر كتير، بس اختي...
• I don’t like the color red much, but my sister...

In other contexts, بس can also mean only or that’s all, so the meaning depends on the sentence.

Because in Arabic, adjectives usually come after the noun, and they match the noun in definiteness. So if the noun is definite, the adjective must also be definite.

• اللون = the color
• الأحمر / الاحمر = the red

So اللون الأحمر means the red color or the color red.

Because -ه means him/it. Here it refers back to اللون الاحمر or more basically the color red.

• بتحب = she likes
• بتحبه = she likes it

Arabic often uses these attached object pronouns where English might also use a separate word like it.

بدها is a very common Levantine form meaning she wants.

It comes from بدّ plus a pronoun ending:

• بدي = I want
• بدك = you want
• بده = he wants
• بدها = she wants

So بدها قميص احمر = she wants a red shirt.

Because it means a red shirt, not the red shirt. The phrase is indefinite.

• قميص احمر = a red shirt
• القميص الاحمر = the red shirt

Again, the adjective follows the noun and matches it in definiteness. Since قميص is indefinite, احمر is indefinite too.

Because احمر describes قميص (shirt), not اختي (my sister).
قميص is masculine, so the adjective is masculine too.

So the structure is:

• بدها قميص احمر
• She wants a red shirt

It does not mean that the sister herself is red.

Yes, it is clearly colloquial Levantine. Some clues are:

• ما بحب instead of Standard لا أحب
• كتير instead of Standard كثيرًا
• بس for but
• بدها instead of Standard تريد
• no case endings

A more Standard Arabic version would sound something like لا أحب اللون الأحمر كثيرًا، لكن أختي تحبه وتريد قميصًا أحمر.

Yes. In casual Arabic writing, especially online or in dialect writing, people often leave out some hamza details and other formal spelling marks.

So you may see:

• اختي instead of أختي
• الاحمر instead of الأحمر

That is very common in informal writing. Also, قميص is often pronounced qamīs, but in some urban Levantine accents the ق may sound like a glottal stop, more like ʔamīs.