Some Macintosh II users with 8-bit or 4-bit video cards and color
monitor, running System software 6.0.2 or 6.0.3 have run into a minor
problem when using the Control panel. Results are different depending on
whether you set video for 256 colors or 16.
For example, select the Control Panel, and then set the card for 256
colors. Now select General and use the arrows above the sample patterns to
move through the predefined options. Create a colored desktop pattern and
change your desktop pattern to the new colored pattern. Now select any one
of the other Control Panel icons (like Mouse, Keyboard, Monitors, Color, or
other), and watch the desktop pattern. If you followed every step, then
you should see no unexpected changes while doing the above steps.
Now, set up your video for 16 colors and do the same steps. You should
notice that the desktop colors change as you step through the various,
predefined, desktop patterns. In addition, they change when you select
other Control Panel devices.
The reason 256-color mode works properly and 16-color does not is unusual
but not an anomaly. The General CDEV uses the standard system "CLUT"
(color look-up table) to define the variety of colors and patterns it
stores as default options. The system color-look-up table contains 256
separate entries or colors. When the system is set to the 16-color mode,
only 16 of the 256 colors are accessible at a given time, and the system
defines 16 colors as the 16-displayable or default colors.
The General CDEV adjusts the 16 default colors to the colors used by its
patterns or the patterns created by the end user, as they are selected.
This adjustment of the 16 default colors remains in affect only as long as
the General CDEV is active. As soon as another CDEV is chosen or the
Control Panel is closed, the 16 default colors revert back to those set as
default by the system, which causes the desktop colors to change.