Demin and different dye colors

Do different colors of fabric dye affect denim differently?

Often, when I buy jeans or denim shorts, I’ll buy two pairs: one blue pair and one black pair. The jeans/shorts are otherwise identical. Almost invariably, once they’ve been washed, the two pairs will fit differently. Specifically, the blue pair will be tighter than the black pair. If I put on a few pounds, I discover that I can still get into the black jeans, but that I can’t even get the blue ones buttoned, despite the two pairs being the same brand, style, and size. Also, the blue pair will start showing stress and wear around the seams and rivets much sooner than the black pair.

Any explanation for this?

Black is a pretty deep dye process. I assume it affects the material differently.

But I seem to remember my (same size and style) black jeans being tighter than my blue ones…