Chokes and Spreads Fill the Gaps
In order to compensate for minor misalignments on the printing press you need to slightly overlap your touching colors. Then, if one color shifts slightly you won’t get a white space (or whatever color your paper is) between colors.
Choke and Spread are similar terms used to describe the process of intentionally overlapping touching colors. Which is which?
First, a general rule of thumb is:
Lighter colors expand into darker colors.
The reason for this is that, to the eye, changes to the darker objects are more noticeable than the slight changes to the lighter object. To determine whether you are applying a choke or a spread will depend on the direction of the color overlap.
In the illustration on this page we use dark blue and pink. The green represents where the pink overlaps the dark blue.
In first example the lighter pink spreads into the darker blue background color. In second example the lighter pink background color chokes the darker blue object in the middle.
The exact terms are less important than understanding which color needs to be overlapped. With multiple overlapping objects it can get tricky.
What actually happens is that one color ends up printing over the other. The slight overlap of color, if done properly, won’t be particularly noticeable. If it does get out of register on the press, the extra allowance of pink will keep a white gap from appearing.