High-contrast colors are colors that are farthest from each other on the color wheel. Examples include: Red and Green, Blue and Yellow, Orange and Cyan.
Monochromatic contrast refers to colors that differ in lightness or saturation but not hue. Examples include: Lightness Contrast, Saturation Contrast.
Isoluminance contrast is when two colors have the same lightness but different hue. Examples include: Red and Blue, Blue and Yellow.
Simultaneous contrast is when two or more colors are presented together, making the contrast appear more intense. Examples include: Red and Green, Blue and Yellow.