Learn Hardcore Arabic (Levantine): ما بحب اللون الاحمر كتير، بس اختي بتحبه وبدها قميص احمر. - I do not like the color red very much, but my sister likes it and wants a red shirt.

Because the verb already tells you the subject. In Levantine, بحب means I like / I love, so أنا is usually omitted unless you want emphasis: أنا ما بحب... = I personally don’t like... English needs I; Arabic often doesn’t.

What does ما do in ما بحب?

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.

What does the بـ in بحب and بتحبه mean?

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.

What does كتير mean here?