“Simultaneous Contrast Illusion (plate4 A&B)- The background is a colour gradient and progresses from dark grey to light grey. The horizontal bar appears to progress from light grey to dark grey, but is in fact just one colour.” (Source: http://en.wikipedia.org/wiki/Optical_illusion ; June 5, 2012)

Plate5 Paul Klee, Polyphonic White, 1930	Plate6 Color Intensity increase the dimension

Plate 5 A&B illustrates the depth of field based on color intensity and transparency of the color.

Plate6 A & B Color transparency and color  illusion

Plate7 Material Transparency & color

Human eyes may experience illusion due to the material transparency against color. The white opaque color reduces the depth of filed while the ice-blue transparent color increases the dimension.