One way to prevent is to start Netscape with the -install switch:
> netscape -install &
This installs a private colormap for Netscape. In some window managers you will experience color flashing as you change the focus from window to window. This occurs because the maximum number of screen colors has already been utilized. For example:
1) The maximum number of supported screen colors is 256.
2) Other applications use up 150 colors.
3) Netscape uses 150 colors.
4) The total number of required colors is 300.
5) The 300 required colors will not fit onto a 256 color map.
Hence, the 'focus' window will use all 150 colors that it needs. Whereas other windows (applications) in the background will request as many colors as possible from the system colormap. (about 106 slots will be open and used) However, 44 colors that have been requested will not be available. Hence, any available colors will be utilized to fill the 44 'orphaned' colors.
This effect is known as 'technicolor.' It is inconsequential and will not hurt the system.
