Colorsets

A Colorset is a collection of colors: foreground (fg), background (bg), hilight (hi), and shade (sh). The foreground is the color of the text, background is the color behind the text, and the hilight and shade are used to give a 3D beveled effect around the border. This causes a raised or sunk look, like a button. Besides just setting the color, Colorsets can use pixmaps, gradients, shape masks and be pseudo-transparent.

Read more: https://www.fvwm.org/Wiki/Config/Colorsets/