Some rockets have black-and-white patterns painted on them. For example, the Saturn V has them at the bottom of the upper stages and the SLS block 2 is supposed to have them below the payload. In contrast, the Delta rockets do not have these patterns.
At least the prototype of the German Aggregat 4 rocket had similar patterns for the purpose of estimating radial motion visually. I suppose that this cannot be the sole purpose of these patterns on more modern rockets since telemetry would provide this kind of data.