A greyscale is the lightness scale where:
It's a color space that has only one parameter which controls the level of lightness going from black to white.
In css with the rgb color function were all primary colors are mixed at an equal level to get an achromatic color
#swatches > * {
width: 4rem;
height: 4rem;
display: inline-block;
margin: 0.5rem;
}
<div id="swatches">
<div style="background-color:rgb(0,0,0)"> </div>
<div style="background-color:rgb(12.5%, 12.5%, 12.5%)"> </div>
<div style="background-color:rgb(25%, 25%, 25%)"> </div>
<div style="background-color:rgb(37.5%, 37.5%, 37.5%)"> </div>
<div style="background-color:rgb(50%, 50%, 50%)"> </div>
<div style="background-color:rgb(62.5%, 62.5%, 62.5%)"> </div>
<div style="background-color:rgb(75%, 75%, 75%)"> </div>
<div style="background-color:rgb(87.5%, 87.5%, 87.5%)"> </div>
<div style="background-color:rgb(100%, 100%, 100%)"> </div>
</div>