Q: How come the inside of jeans have different colors?
The different colors are due to two different weft colors. Denim fabric is made up of alternating woven yarns, the “warp” and the “weft“. The warp yarns that show up on the outside and are typically dyed indigo, while the weft yarns are on the inside and are typically white.
However, not all denim jeans have these colours such as with black jeans (i.e. black warp and weft yarns) or double indigo jeans (e.g. indigo warp and weft). Since the weft is considered the “filler” yarn too, some companies will use a slightly off-white yarn leading to an off-white colored interior.