A few figures showing different color interactions. Notice how the figure seems to get brighter in places where red overlaps black a phenomenon the ties in with Moire patterns. These points lead to the impression of lighter lines. Do these "lines" appear perfectly vertical?
As a different effect, notice how the array of black lines does not seem to be ordered exactly vertically.
The figure below is similar, but it show more strongly that there seems to be an orange cast over sections of the figure and that the background is not white.
Also, the green lines do not seem to be arrayed perfectly horizontally
The smaller gray in the patches below are both the same hue and are both "neutral" gray.
The type of mark affects perceived color. Perhaps since this effect has long been known, many fail to mention it.In the figure below, the central portion of all of the dots is the same, yet the dots appear to become less saturated from top to bottom.
Another example with different hues.
An example of contrast. Both ovals are the same.
