That bit about the face on the cover changing how you see the character is spot on. I always pictured Gatsby one way from the common blue cover, but seeing the original art with those sad, tired eyes made me rethink him completely. It's like @angela587 said with Dune's colors, the first design sets a mood. Now I wonder how many other books I've judged by their later, wrong covers.
That bit about the "sad, tired eyes" really hits home. It makes you realize how much a cover can twist your whole reading of a character. I'll be checking first edition art from now on before I start a book.