Translation:Our boots are not black, but brown.
Bakancs and csizma are different kinds of boots. You can google a few pictures to see the difference, but the baseline is that bakancs usually have a shorter shaft and have laces.
I'm having trouble discerning whether the noun is singular or plural. What would be the difference between 'our boots are not black, but brown' and 'our boot is not black, but brown'?
It's singular. In Hungarian bakancs can mean a "pair of boots", so even though it is singular in Hungarian, the English translation should be plural. If you really want to talk about one boot, you usually need to emphasize that it's just one (egy darab bakancs) or perhaps specify which one you mean (a bal/jobb bakancs.)
Sorry, that is a bit tricky...
Our boot, singular: "bakancsunk"
Our boots, plural: "bakancsaink"
So, when it is a possessive ending, look for the letter "i". I know, it is more complicated than that, but that's a good first clue.
This is just the grammar part of it. But things in pairs can be referred to in the singular in Hungarian.