Its not blacker than black, it's just almost true black. Everything else you can see that you think of as black is merely very dark grey.
Then at the other end you have white, which is kinda light grey and you can get whiter than white....
As for painting a car in that stuff, it would look like a cardboard cut out black hole in the profile of your car. i.e you wouldn't be able to see any shape detail, just the outline, so in theory you would be able to see the shut lines or door handles and it would be even harder to work out where the bonnet ends when sitting inside it.