Drawing in the foreground color.

Use the default, or specify :ink +foreground-ink+.

Erasing.

Specify :ink +background-ink+.

Drawing in color.

Specify :ink +green+, :ink (make-rgb-color 0.6 0.0 0.4), and so forth.

Drawing an opaque gray.

Specify :ink (make-gray-color 0.25) to draw in a shade of gray independent of the window's foreground color. On a non-color, non-grayscale display this will generally turn into a stipple.