APPENDIX FIVE
Color
Color is a very important aspect in the Atari computers; you may not
fully appreciate it unless you've spent a long time working with
computers or monitors with monochrome displays. The Atari has
sixteen colors available for display in eight different luminance
(brightness) factors. These colors are stored in memory locations 704
to 712. The first four of these registers are used to determine the color
of your players and missiles. The second five determine the color of the
playfields, background, lines drawn and areas filled.

The Atari has a default value for each of the five playfield registers that
is assigned on powerup:

Playfield   Location  Color            Value
0           708       Orange             40
1           709       Light green       202
2           710       Dark blue         148
3           711       Red                70
4 (BAK)     712       Black               0

The figure in the value category represents the number you would get
if you PEEKed into that location. For discussion of the locations, refer
to the Memory Map.

To change these colors, you can use either a POKE statement or the
BASIC command SETCOLOR (abbreviated to SE). You should refer to
the description in the earlier Memory Map text. SETCOLOR has three
parameters: the register to change (which always corresponds to one
of the memory locations above); the hue (a number from zero to fifteen
which corresponds to the available colors); and the luminance (an
even number between zero and fourteen). The Atari will treat any odd
number as if it were the next lowest even number where luminance is
concerned. Your statement might look like this:

SETCOLOR 0,2,8

This will produce the orange color in playfield zero. To change it to
red, you would use:

SETCOLOR 0,4,6

Unless you are changing the background or border or you are
changing a register which has already been used for drawing on the
screen, you won't see any change from using SETCOLOR. The effect
comes when you follow up with a COLOR command, telling the Atari
which register to use for the DRAWTO or fill command. You can easily
POKE the location with the proper color value by using this formula:

COLOR = HUE * 16 + LUMINANCE

So the orange in the above example would be obtained by:

POKE 708,40

and the red by:

POKE 708,70

These are the values listed in the chart above. It's quite simple to
change them to your own colors using either method. Of course, you'll
have to adjust your colors every time you change GRAPHICS modes
or press RESET, since both restore the registers to their default values.
What's more, the player/missile registers can only be changed using
POKE; they have no corresponding SETCOLOR commands and are
all preset to zero. The winter 81/82 edition of The Atari Connection,
the house organ of Atari Inc., had a nice little chart in full color to
display all of the colors available. The SETCOLOR number in the
following list is the value you would place as the second number in the
statement right after the register number.

                      SETCOLOR       POKE
Color                   number      number
Black                      0           0
Rust                       1          16
Red-orange                 2          32
Dark orange                3          48
Red                        4          64
Dark lavender              5          80
Cobalt blue                6          96
Ultramarine blue           7         112
Medium blue                8         128
Dark blue                  9         144
Blue-grey                 10         166
Olive green               11         176
Medium green              12         192
Dark green                13         208
Orange-green              14         224
Orange                    15         240

The next number in the SETCOLOR statement would be the
luminance. You would add the luminance value to the POKE number.

When you want to use the DRAWTO or XIO 18 (FILL) commands, you
must first specify what color register to use by the COLOR command.
The confusing part for most people is that the number in the COLOR
command doesn't correspond to the same number as the SETCOLOR
register and, to make things worse, it's not always the same number in
different GRAPHICS modes! Modes zero, one, and two are text
modes; they print characters to the screen rather than graphics, so you
don't use the COLOR command in these modes. In GR.0, you actually
have only one color as chosen by SETCOLOR 2. The luminance is
ignored in this command and is instead set with SETCOLOR 1 --
where the color is ignored. You can use SETCOLOR to change the
colors of the text and the background as below:

GRAPHICS 0                    SETCOLOR     Register
Character luminance              1           709
Background                       2           710
Border (BAK)                     4           712

GRAPHICS 1 and 2              SETCOLOR     Register
Uppercase and numbers            0           708
Lowercase characters             1           709
Inverse uppercase                2           710
Inverse lowercase                3           711
Background, border               4           712

When you want to draw or fill an area in modes three to eight, you must
use the proper COLOR statement for the SETCOLOR register:

GRAPHICS 3, 5, 7           SETCOLOR       COLOR   Register
Four color modes
Graphics point or             0             1       708
fill area                     1             2       709
                              2             3       710
Background, border            4             0       712

GRAPHICS 4, 6              SETCOLOR       COLOR   Register
Two color modes
Graphics point                0             1       708
Background, border            4             0       712

GRAPHICS 8                 SETCOLOR       COLOR   Register
One color, two luminances
Graphics luminance            1             1       709
Background color              2             0       710
Border                        4            --       712

It's awkward, but not difficult to use. You will have to refer to this chart
or the chart on page 53 of your BASIC Reference Manual until you get
the hang of it. Remember to precede any COLOR statement with a
SETCOLOR somewhere in your program and to precede a DRAW or
XIO 18 with a COLOR or the computer will use the previously
designated register.

The GTIA chip confuses things somewhat: in GRAPHICS 10, register
704 stores the background color while 712 is used as a normal color
register. This means you must change it with a POKE rather than a
SETCOLOR statement. However, in the two other GTIA modes (GR.9
and GR. 11), you still use location 712, SETCOLOR 4, for the
background; see the examples of GTIA modes at location 623.
With GRAPHICS 9, the COLOR command is used to set the luminance
level to one of sixteen possible values; the value you use with the
COLOR statement is equal to the luminance used (so you can have
COLOR 15, COLOR 10, etc. Actually you can use any value up to 255
with COLOR and not get an error message; see the demo program for
GR.11 in location 623). SETCOLOR 4 defines the background and
graphics color. There is only one color in GR.9. In GRAPHICS 11,
COLOR is used to define the color the same way it is used for
luminance in GR.9, while the luminance of each color is the same
value; you can have sixteen colors all of the same luminance.
GRAPHICS 10 allows you to set the nine color registers to individual
colors and luminances, but you must use POKE commands for the
registers 704 to 707.

For more information on the GTIA modes, see COMPUTE!, July to
September 1982, and De Re Atari. There are many good programs for
drawing your own pictures in various GRAPHICS modes;
Micropainter from Datasoft is one of my favorites; then there's Drawpic
from Artworx, The Graphics Machine from Santa Cruz, Graphic
Master from Datasoft, Graphics Composer from Versaware and The
Next Step from Online which is really a utility for character creation
and color set selection. COMPUTE! published an interesting program
called "Supercube" over many issues in 1980 and 1981.