Translation:My suitcase is green, not red.
Wait, what? So you would call this:
Guess it's another case of Polish differentiating something that English doesn't, like 'cap – hat', 'jacket – coat' and so on. ;)
In the sense of collecting one's bags from the baggage carousel in an airport, then yes, I'm with Jack on this one.
Is a "walizka" always rigid? As it happens, the English (well, probably French) "valise" can be rigid or soft-sided.
Incidentally, I would for sure differentiate betwixt a "cap" and a "hat".
Yes, that's what differentiate it from „torba”(bag) – though how 'rigid' it is, can vary, some have double skin or cardboard frame, so they aren't that 'rigid' – nevertheless, the fact they have any frame at all is what makes them into „walizka”. ;)
Why is "My suitcase is green, it isn't red" wrong?
The second clause doesn't use any form of 'to be'. It's just 'green, not red'.