The Chubb illusion is an optical illusion wherein the apparent contrast of an object varies dramatically, depending on the context of the presentation. Low-contrast texture surrounded by a uniform field appears to have higher contrast than when it is surrounded by high-contrast texture. This was observed and documented by Chubb and colleagues in 1989.
In short, the circle in the right appears more clear than the circle in the left.
Again, u can cut and put both the circles separated from those Grey colors to check