HWB is a new color standard in CSS4. It was founded by the same person, who had invented HSL. The aim was to make it easier in usage. Definitely, it is. Unfortunately, it’s a working draft yet.
HWB includes Hue, Whiteness and Blackness.
If you use HSl, you must be familiar with Hue. It is composed of the rainbow colors: starting with red and ending with violet. From violet it returns to red making 360 degrees. Hue specifies an angle starting at 0 with red.
Whiteness and Blackness
In contrast with HSL, in HWB to reach the desired colors, you should specify the hue and leave Whiteness and Blackness to zero. It’s quite easy in usage: black is too dark, white is too light. The more black you add, the darker your desired color will be. In case you add as much white as you add black, your final color will appear grey.