At this point in the process, I think the only solution is to install more of the darker colored tile along the entire short wall (meaning the whole wall behind the hood).

I hope this is feasible? The wall itself may have to be gouged out a bit in order for the tile to lie flush.

I'm sorry to say this but I don't think a patch job is going to do your kitchen justice. Your tile is expensive as well as the hood. Perhaps one of them needs to go. If you are determined to keep both, perhaps take good down hood and install the light tile over the whole wall. With the hood jutting out at an angle, trying to fill in the gap isn't going to solve this issue.

Hi! Sorry you are having issues. I believe that somehow your vent hood was assembled improperly or installed improperly. I have never seen lights at the very back of a vent hood. They should be at the front of the hood. At any rate, Contractor should have shimmed it out or something to make it straight. Not saying that shimming is the answer, I just can't understand how a contractor would call that acceptable. Double check the install and assembly. Do you have any photos of the unit in the package? Or maybe look up the model number online? I bet you will see the lights at the front of the hood. Maybe not, but maybe. Good Luck!! Attached photo is my new hood with lights at front. (The model is my Handsome Nephew cooking Christmas Breakfast)

I took my own advice and looked it up. I guess it does have lights at the back. I guess I would go up with the dark tile. That is strange and I would not be happy about having my hood be on an angle like that. Maybe you could return the hood and get another?

It would be relatively easy to add a layer of 5/8 drywall behind the hood as wide as the backsplash, and painted the same as the wall.

There is even a bullnose profile that would fit in with the tile edge.

http://www.gordon-inc.com/interiors/finalforms/drywalltrim/specialshapes.aspx

It would just give an interesting detail without adding any visual heaviness.