The Bezold Spreading Effect tool demonstrates the phenomenon of assimilation, which results in the difference between neighbouring colours being reduced by »overexposure«.
For this purpose, the computer screen is divided into two different areas whose colours can be changed interactively. Within each of the two colour areas there is also a group of longitudinal stripes of the same colour, which can also be changed independently of each other.
Depending on the surrounding colour, a different colour impression is created, although the longitudinal stripes are physically identical. The colour of the longitudinal stripes changes in the direction of the surrounding colour.
To verify that the vertical stripes are actually the same colour, they can either be moved to the left or right colour field or the background colour can be hidden.