The shade of the bar looks invariant in isolation but variant in context, in (favor of) sharp contrast with the color gradient background, hence an innateillusion we have to reasonably interpret and overcome as well as the mirage. Such variance appearing seasonably from context to context may not only be the case with our vision but worldview in general in practice indeed, whether a priori or a posteriori. Perhaps no worldview from nowhere, without any point of view or prejudice at all!
Ogden & Richards (1923) said, "All experience ... is either enjoyed or interpreted ... or both, and very little of it escapes some degree of interpretation."
H. G. Wells (1938) said, "The human individual is born now to live in a society for which his fundamental instincts are altogether inadequate."