A lot of the information here is clearly deflecting from the grandfather's carelessness (I won't go so far as to say "recklessness"). First off, he's not elderly--he's 51. That's not that old! While he could possibly have some medical conditions, he's likely got a few decades left in him.
Secondly, even if he's color blind, he would see tones. When someone cant' see, say, the color red, they don't see nothing, they see gray. So, even assuming he was color blind and cannot differentiate the color blue (the tint of the windows), he would still be able to recognize that they were tinted, but might think that they're tinted gray. So, he could discern the tinting, regardless.
I know that a lot of the people on this thread, myself included, have never been on Freedom of the Seas (or one of her sister ships). However, when I watch that video, it's clear that (a) the railing is several inches away from the windows, (b) there was glass at floor height, where a child could press on the glass if she so desired, (c) the pool/children's area is not near the walkway/railing/windows, and (d) the tinted windows are very obvious.
The grandfather had a lapse in judgement here. If the child's feet had stayed on the ground, she would have been fine. My heart breaks for the entire family, and I don't think for a second that the grandfather did anything with any kind of bad intent. It was a horrible, tragic accident. But, 100%, he's at fault. If I were on the jury, I'd convict, but argue for mercy in the punishment phase.