GIMP has four kinds of brushes:
Ordinary brushes have no specific name. They are shown in the Brushes dialog as small grayscale images called pixmaps. When painting with the ordinary brushes, the current foreground color is used, with the intensity of the color represented by the intensity of black in the pixmap.
Figure 22-37. Building an ordinary brush
Color brushes are represented by a color pixmap in the Brushes dialog. Internally, they are represented by this pixmap, as well as by a grayscale copy of this pixmap, which serves as a mask. When used with paint dynamics without any box checked in the Color row (see Drawing ...