pfr I found manpages on the web that describe xsetroot with support of setting xpm files as background. However, the version on NetBSD doesn't have this feature (and neither does the one on my Linux workstation).
You can sort-of work around this by using an XBM bitmap file and setting the foreground and background colors in the command. An equivalent to your XPM would be the following.
test.xbm:
#define test_width 3
#define test_height 3
static unsigned char test_bits[] = {
0x00, 0x02, 0x00};
And the command:
xsetroot -bitmap test.xbm -bg '#8998aa' -fg '#464d56'
There is a graphical bitmap editor called bitmap present by default if you want more elaborate creations. However, you're still limited to two colors.
