the default [Black] swatch (0/0/0/100 in CMYK) really is a lighter color than a rich black mixed from four CMYk ink, or 3 RGB colors. It would be pretty unusual to see a black background in an image that wasn't a mix.
Do you have the preference in ID for Appearance of Black set to Display All Blacks Accurately? That will show you the difference in ID on screen as well.