The Celeste McCollough effect is a phenomenon of human visual perception, in which these black & white lines appear coloured, depending on their orientation.
It is an after-effect, that requires a short a period of induction to produce it.
For example, if you look at the red horizontal lines for a few minutes, and then back to the black and white lines, you will notice an after-effect.
The black-and-white horizontal lines will have a tinge of green and the black-and-white vertical lines will appear pink. This effect was discovered by Celeste McCollough in 1965.
I love Optical Illusions. I hope you do. My name is Steve Howard. You have been reading the digital circus.