Seems that gtk is no longer compatible with 8 bit displays.  I'm running on a
NetBSD-2.0/alpha box but the display is set to a Solaris-2.9/sparc box
(Ultra/10) that only has an 8 bit display.  I have

gtk2+-2.8.20
cairo-1.2.0

When I run even a simple program like the gtk-demo program which comes with gtk,
I get the following:

% gtk-demo
Error: Cairo does not yet support the requested image format:
        Depth: 8
        Alpha mask: 0x00000000
        Red   mask: 0x00000000
        Blue  mask: 0x00000000
        Green mask: 0x00000000
Please file an enhacement request (quoting the above) at:
http://bugs.freedesktop.org/enter_bug.cgi?product=cairo
assertion "NOT_REACHED" failed: file "cairo-image-surface.c", line 144, function
"_cairo_format_from_pixman_format"
Abort


When I display to a different X server that has more colors then things work. 
Unfortunately, my ultra/10 is one of my primary systems and upgrading to a true
color display is just not in the works.