eChalk colour perception: This is the most amazing optical effect in the world Our perception of color is strongly affected by the coulors surrouning it. In fact it is possible to perseive two identical colors as being very different is the are placed on different backgrounds. Quite simply these are some of the most staggering optical effects I have ever seen. I guarantee you will not believe your eyes. eChalk's online optical illusions, educational games, teaching resources and lesson activities for interactive whiteboards and data projectors will inject some fun into your classroom. in coolwith colorfunillusionillusionsinteractifopticalvisualby 2 users