Bit-Plane Assignment In Dual-Playfield Mode - Commodore Amiga Hardware Reference Manual

In dual-playfield mode, each play field is formed from up to three bit-planes. Color regis-
ters 0 through 7 are assigned to playfield 1, depending upon how many bit-planes you
use. Color registers 8 through 15 are assigned to playfield 2.
Bit-Plane Assignment in Dual-playfield Mode
The three odd-numbered bit-planes
(I, 3, and 5) are grouped together by the hardware
and may be used in playfield
1.
Likewise, the three even-numbered bit-planes (2, 4, and
6) are grouped together and may be used in playfield 2. The bit-planes are assigned
alternately to each playfield, as shown in figure 3-13. Note that in high-resolution mode,
you can have up to two bit-planes in each playfield - bit-planes 1 and 3 in playfield 1
and bit-planes 2 and 4 in playfield 2.
60 Play field Hardware