In the picture above, the same horizontal striped pattern has been added to all of the square backgrounds, yet the pattern is much harder to see on the left. These examples demonstrate the three main background properties that affect human ability to see objects: the luminance, the contrast and the similarity of the background to the orientation and shape of the object.
Sebastian, S., Abrams, J. & Geisler, W. (June 26, 2017) Proc. Natl. Acad. Sci. USA.