Nothing whatsoever. It's just a white kitty.
I've heard of a black cat crossing your path to be a sign of bad luck, but I've not heard anything about black and white cats. In any case, it's just superstition, it doesn't mean a thing.
It means they might be friends, or mates, or maybe they are just walking together. Or did you mean bad luck/good luck coming your way? because it looks like you are evenly balanced then.
Nothing
If you mean the musical, it is the white cat.
No because in order to see anything light has to be reflected off of it. If it is pitch black no light is there to be reflected off the white cat.
Emphatically yes.
Black cat roll on Bed white cat see and said you look beautiful :P
Cats can see in colour. yes they can so can dogs
Bad Luck
It pretty much just means the cat felt like it.
A white cat can be of any breed. It is simply a white cat.
Nothing.