I applaud the idea.
Though if you're looking to reinsert all deleted scenes, you should be aware that a hefty amount of footage is present in the film trailers while completely absent from any special features. For instance: in the Half-Blood Prince trailers, there's a shot of Ginny being disarmed of her wand that isn't in the final cut (the funny thing is that if you look closely in the film you can see Ginny pick it back up again). In another trailer, Snape mutters, "It's over," as he watches Dumbledore falls dead from the tower.
There's a comprehensive list of all sorts of unreleased deleted scenes here if you're interested (most of them are just images, but it's fun to look through).
I'm also glad to find someone who doesn't like the colors of the last few films too. My biggest issue is that they're so dark, to the point where you can barely see anything at some points (especially in DH1).
If I could make some suggestions:
- Add Hedwig's Theme in to the beginning of DH2. I think I died a little inside when I saw that the film completely disregarded this tradition in favor of Lily's Theme.
- If you're going to add in the deleted scene in Chamber of Secrets where the Grey Lady is humming as Harry is trying to read Tom Riddle's diary, maybe you could try to make her look the way she does in DH2. I don't know if this is even possible, or what your or the program's limitations are, but it's something to consider.
- This is a personal preference, but maybe you could try to do something about that idiotic opening scene in Half-Blood Prince where Harry and that coffee shop girl set up a date. I can't believe Harry would be so much of a numbskull that he'd bring a Daily Prophet into a muggle coffee shop and then not hide it when the girl came along. Maybe you could at least remove the line where she mentions that she saw a picture move, to imply that muggles just can't "see" the pictures the same way wizards can. It's just something that's irked me for a while.
Also, when you mention matching the visual styles, what style do you have in mind? For what it's worth, I've always felt that the supernatural occurences in first two or three films actually feel like magic; the other movies I feel treat the magic like pure science fiction (especially in the last two movies). Just my personal preferences at work again, but I'm interested to hear what your preferred style is (and what you hope to do with the films that don't match it).