Invisible is another way of saying perfectly transparent, meaning that it neither absorbs nor reflects photons. Something that absorbs all photons is just black.
That would make it extremely dark, not invisible. In order for it to be invisible, it would have to bend the photons in a way that it's original path was uninterupted. that would give it the appearence that it isn't there! +1
also it is not invisable because it would still create a shadow
this is why we don't try to apply real world physics to fictional materials/ objects