Simultaneous Contrast
Simultaneous Contrast is when a color brings out its complement in a color adjacent to it. In the first square the neutral color appears darker and cooler because the orange brings out the qualities of its compliment, blue, therefore the neutral color appears cooler than darker. In the second square the neutral color appears brighter and warmer against the dark green because the green brings our the qualities belonging to its red compliment, therefore the neutral color appears brighter and warmer.
Each example changes how we perceive color because of the placement and proportion of colors display contrast in hue, value, and color. The more surrounded a light color is by a dark color, the brighter the light color and appear and vice versa.