The two rings are identical, but the one on the right stands out from the background much more strongly, in addition to appearing metallic or lustrous compared to the matte or dull ring on the left.

Simultaneous contrast this apparently works to enhance figure-ground separation.

Standard models of perception that map intensity to a continuum of grey shades ranging from black to white (absolute gamut) predict that the induced brightness and darkness from the background should cancel and the rings should appear identical.