Am I correct in assuming that the added scenes have a slightly darker color tone and appear more grainy throughout the feature?

Yes you are

But big deal,it didn't stick out as bad as people make it seem. Besides the film has an intentionally grainy/soft image. So it fits right in,in my opinion.

Damn, I didn't even notice this. Then again, it was probably more than a year after I saw the film in theatres that I watched the DVD, so I didn't remember well what wasn't in the theatrical release.
It's not quite as good as the original, but actually a pretty decent remake.

Never saw it in the theatres, and never noticed the image quality switch. To be honest with you, I didn't really look for it, either.

And at the danger of being skewered over the interweb, my roomates and I fell asleep watching the original. (We did start it at like 1 AM to be fair).

I wish the movie was extended to show the scenes when they arrived at the island, instead of getting bits and pieces during the credits. Pretty good movie though.

I never noticed any difference.