For three or more colors, you need more than one bitplane. The task here
is to define each bitplane in such a way that when they are combined for
display, each pixel contains the correct combination of bits. This is a
little more complicated than a playfield of one bitplane. The following
examples show a four-color playfield, but the basic idea and procedures
are the same for playfields containing up to 32 colors.

Figure 3-8 shows two bitplanes forming a four-color playfield:


        Image in                          Results in a display
       bitplane 2            _____          similar to this:
                            |     |
            +---------------- 0 1 | Color 1 -------+
            |               |___ _|                |
            |                   |                  |
            |                   |                  |
          +---+               +---+                |
     0 0 0|0 0|0 0 0     0 0 0|1 1|0 0 0          ***
          |   |               |   |               ***
     0 0 0|0 0|0 0 0     0 0 0|1 1|0 0 0          ***
          |   |               |   |               ***
     0 0 0|0 0|0 0 0     0 0 0|1 1|0 0 0          ***
          +---+               +---+               ***
     1 1 1 0 0 1 1 1     1 1 1 0 0 1 1 1    ······   ······
                                            ······   ······
     1 1 1 0 0 1 1 1     1 1 1 0 0 1 1 1    ······  \······
          +---+               +---+               ···\
     0 0 0|1 1|0 0 0     0 0 0|1 1|0 0 0          ··· \
          |   |               |   |               ···  \
     0 0 0|1 1|0 0 0     0 0 0|1 1|0 0 0          ···   \__   Color 00
          |   |               |   |               ···       (background)
     0 0 0|1 1|0 0 0     0 0 0|1 1|0 0 0          ···
          +---+               +---+                |
            |                   |                  |
            |                ___|_                 |
            |               |     |                |
            +---------------- 1 1 | Color 3 -------+
                            |_____|


                 Figure 3-8: Combining Bitplanes


You place the correct "1"s and "0"s in both bitplanes to give each pixel
in the picture above the correct color.

In a single playfield you can combine up to five bitplanes in this way.
Using five bitplanes allows a choice of 32 different colors for any single
pixel. The playfield  color selection charts  at the end of this chapter
summarize the bit combinations for playfields made from four and five
bitplanes.