Recently when I look at old quicktime movies I've made, they are pixelated in very few colors kind of an Andy Warhol look. They never looked that way when I made them years ago.
I just made a new Quicktime with the same results.
Youtube converts your clip to another format, so it sounds like it's your copy of quicktime that is bung, not the clips themselves. Did you try the same clip on another computer somewhere?