Matte surfaces reflect light at a random angle, whereas glossy surfaces reflect it light like a mirror, at what’s called the angle of incidence, which more or less is the angle something bounces off a flat surface.
The darkness of a color is determined by the percentage of light reflected, with smaller percentage creating darker colors.
Something that only reflects a small percentage of the light, but that reflected light bounces the same way light bounces off a mirror, will be dark and glossy.
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