Akiyoshi Kitaoka, a professor of Pyschology at Ritsumeikan University, Kyoto, Japan, and the famed creator of the Rotating snakes illusion, has been updating his site since 2002 and it is full of intriguing color illusion. He is also responsible for inspiring the artwork on Animal Collective's Merriweather Post Pavilion album.

Four Tanks

There are two pairs, each of which consists of two squares of the same color. Which are the two pairs?
Answer of "Four tanks": the pair of the leftmost square and the neighboring one, and the pair of the rightmost square and the neighboring one

Squares of four colors

Copyright Akiyoshi Kitaoka 2007 (February 15)

It appears that there were squares of four colors, though there are two colors (red and green) for squares.

Realistic Shiosai*

Copyright Akiyoshi Kitaoka 2008 (August 22)

*The sound of the sea

There are two colors of half doughnuts, dark or light, though they are nealy the same color as each other. The original illusion is Professor Adelson's modulation of the Koffka ring.

Light of Sapphires

Copyright A.Kitaoka 2004 (June 18)

Blue dots appear to scintillate.

Sakai's color contrast

Copyright A.Kitaoka 2002

The squares of the upper row appear to be gray, but they are tinted as shown in the lower row that exchanges between the left fives and the right fives. This illusion is based upon a finding of Kasumi Sakai's graduational thesis (2003, Department of Psychology, Ritsumeikan University) entitled "Color representation by Land's retinex theory and Belsey's hypothesis" (in Japanese).

Illusory Red Ring

Copyright Akiyoshi Kitaoka 2006 (June 26)

This image is painted only with cyan (greenish blue) pixels of different luminance and different saturation, but an illusory red ring is observed.

Color contrast? Color constancy? Land's two-color method? Goethe's color shadow phenomenon?

Valentine Gift

Copyright Akiyoshi .Kitaoka 2007 (January 12)

There appear to be pink hearts and orange ones, though they are identical in color (both are pale red).

In Japan, Valentine's Day is a day when girls give chocolate to boys. I do not know what made such a funny custom. On the other hand, the day when the happy boys give gifts back to the girls is called White Day (March 14). For boys who fail to get chocolate, Valentine's Day is the worst day in their life.

cf. Dungeon illusion: Bressan, P. (2001) Explaining lightness illusions. Perception, 30, 1031-1046.

Guruguru 5

Copyright Akiyoshi .Kitaoka 2007 (January 15)

There appear to be two different colors in inner rings, though they are the same as each other.

An Intermediate Color Ring

Copyright Akiyoshi Kitaoka 2006 (August 30)

The color of the ring pointed by an arrow in the left image is the same as that in the right image, but they appear to be different from each other.

Spirals of Color

In each image there appears to be two different colored spiral when in fact there is only one.

See another post on Colorful Optical Illusions.