HP PCL/PJL reference (PCL 5 Color) - Technical Reference Manual

EN Modifying Output Color (Color LaserJet, 5, 5M, DeskJet) D-15
As shown below, the 256 point-by-point transformation curve for each
primary color is defined sequentially for a total of 768 bytes, with the
additional 2 bytes for specifying the color space and reserved data
field.
Byte 15 (msb) 8 7 (lsb) 0 Byte
0 Color Space Reserved Data Field 1
2 Color Component 1, Index 1 Color Component 1, Index 2 3
4 Color Component 1, Index 3 Color Component 1, Index 4 5
. . .
256 Color Component 1, Index 255 Color Component 1, Index 256 257
258 Color Component 2, Index 1 Color Component 2, Index 2 259
260 Color Component 2, Index 3 Color Component 2, Index 4 261
. . .
512 Color Component 2, Index 255 Color Component 2, Index 256 513
514 Color Component 3, Index 1 Color Component 3, Index 2 515
516 Color Component 3, Index 3 Color Component 3, Index 4 517
. . .
768 Color Component 3, Index 255 Color Component 3, Index 256 769