Naive question about color in SunView

[Jack Hwang]

I just entering the programming world for SunView.  I am writing a program
to display a raster picture inside of a Canvas.  I set the Canvas to be
retained, and thus avoiding the trouble to repaint it from time to time.
The program runs well in monochrome system.  But there are problems in
color systems.  The region destroyed by other windows becomes blank, not
retains the original picture; whenever resizes, it has the same problem.
Could anyone give me some direction?  I have looked the sections in
SunView Programmer's manual about pixwin and canvas, but come out with no
solution.  The most confused is : it runs well in monochrome, and it seems
fine in the color system -- if it is not covered by the other windows.

Thanks in advance