Why do printed color layers need alignment?

A multicolor print may be built from several separate passes, with each pass adding one part of the design. The parts must land in their intended positions to make the final picture. Registration is the alignment that makes those separately placed layers fit together.

The example has an outer ring in one color and an inner ring in another. The design intends them to share a center. If the second layer shifts right, it no longer sits evenly inside the first ring. Neither ring has to change shape or size for the combined arrangement to be wrong.

Registration marks provide shared landmarks outside the main design. When corresponding marks coincide, they help show that the layers have been positioned together as intended. This is useful when no single feature inside a complicated picture provides an obvious alignment point. Removing or hiding the marks afterward does not undo a positional shift.

Good registration therefore depends on the relationship between layers, not simply on each layer looking correct by itself. The aligned example keeps the intended common center. This positional issue is separate from the way colored inks interact and from the reversal produced by a direct printing face: a print can have the right individual shapes and colors yet still put them in the wrong places.