Some small questions
>> Q: Can I say: but it looks nice "for" the skirt with the same meaning? Which means replace "with" with "for"?
No, you can't. It has to be with. 'It looks nice with...', 'it goes (well) with...'. If you want to omit the preposition, you can say, 'it matches' as in your next example.
>> A: No, a blue sweater, the same blue that's in the skirt.
>> Q: In the last sentence, can I just omit "that's"? So the sentence would be "the same blue in the skirt".
No, you can't. As an alternative to 'that's', you could say 'the same blue as (in) the skirt', but not 'the same blue in the skirt'.
You can say, "No, a blue sweater, the same blue in the skirt." But that would be very conversational and ungrammatical. In quick, informal, sloppy speech it is not uncommon for "necessary" elements to be omitted. I do not know whether or not there are any "rules" for what can be omitted in cases such as this. I would not recommend that you spend too much time trying to learn to speak this way, though.