the expected color and luminance for a pixel. COLPF3 $D019 Write SHADOW: COLOR3 $02C7 Color/luminance of Playfield 3 COLPF3 is available is several special circumstances: When Missiles are converted to the "fifth Player" they switch from displaying the color of the associated Player object to displaying COLPF3 and change priority. See PRIOR/GPRIOR register. Playfield Text Modes 4 and 5. Inverse video characters (high bit $80 set) cause CTIA/GTIA to substitute COLPF3 value for COLPF2 pixels in the character matrix. (See ANTIC's Glyph Rendering) Playfield Text Modes 6 and 7. When the character value has bits 6 and 7 set (character range $C0-FF) the entire character pixel matrix is displayed in COLPF3. (See ANTIC's Glyph Rendering) This register is also available in GTIA's special 9 color, pixel indirection color mode. COLBK $D01A Write SHADOW: COLOR4 $02C8 Color/luminance of Playfield background. The background color is displayed where no other pixel occurs through the entire overscan display area. The following exceptions occur for the background: In ANTIC text modes 2 and 3, and map mode F the background of the playfield area where pixels may be rendered is from COLPF2 and the COLBK color appears as a border around the playfield. In GTIA color interpretation mode $8 (9 color indirection) the display background color is provided by color register COLPM0 while COLBAK is used for Playfield pixel value $8. In GTIA color interpretation mode $C (15 colors in one luminance level, plus background) uses COLBK to set the luminance level of all other pixels (pixel value $1 through $F). However, the background itself uses only the color component set in the COLBK register. The luminance value of the background is forced to 0. Color Registers' Bits: The high nybble of the color register specifies one of 16 colors color ($00, $10, $20... to $F0). The low nybble of the register specifies one of 16 luminance values ($00, $01, $02... to $0F). In the normal color interpretation mode the lowest bit is not significant and only 8 luminance values are available ($00, $02, $04, $06, $08, $0A, $0C, $0E), so the complete color palette is 128 color values. In GTIA color interpretation mode $4 (luminance-only mode) the full 16 bits of luminance values are available for Playfield pixels providing a palette of 256 colors. Any Player/Missile objects displayed in this mode are colored by indirection which still uses the 128 color palette. In normal