The handling of colors in the drivers is rather confusing. There are a
variety of different systems for referring to colors, with various
tables and other conversions being involved. The different types of
color specifiers are:

1. "internal". Used within the driver. In the PNG driver, this is the
actual 32-bit 0xAARRGGBB value written to the framebuffer. In XDRIVER,
this is either:

a) the actual X Pixel value used by XSetForeground() etc (in FLOAT
mode or for TrueColor/DirectColor visuals), or

b) the index into the xpixels array (in FIXED mode for other visuals),
which maps either gray levels or indices into the color-cube palette
to actual Pixel values.

2. "fixed". An index into the fixed color table maintained by the
library. The table can be modified using LIB_assign_fixed_color() or,
in FIXED mode, COM_Reset_color[s].

3. "float". An index into the (hardware) palette used by the driver in
FLOAT mode. The internal value is obtained by adding the color offset
and the maximum number of standard colors to the float value, modulo
the total number of colors in the hardware palette. 

The hardware palette can be modified using COM_Reset_color[s] (only in
FLOAT color mode).

"fixed" and "float" colors can be translated to "internal" colors
using LIB_get_color_index[_array].

4. "standard". An index into the standard color table maintained by
the library. The table is initialized using LIB_assign_standard_color()
to contain the 13 standard colors defined in colors.h; it cannot be
modified by clients.

5. "absolute" RGB values, in the range 0-255. These values will be
written directly to a 24-bit framebuffer or palette, or scaled for
lower bit depths.

6. "logical" RGB values. These are indices into the R/G/B translation
tables set using COM_RGB_set_colors(). The values passed to
COM_RGB_raster() are logical values.

void DRV_color(int color)
	color:	internal color number

int DRV_get_color(void)
	return:	internal color number

void DRV_reset_color(int color, int r, int g, int b)
	color:	internal color number (palette index; only used in FLOAT mode)
	r,g,b:	absolute R/G/B values

int DRV_lookup_color(int r, int g, int b)
	r,g,b:	absolute R/G/B values
	return:	internal color number

void COM_Color(int color)
	color:	fixed color number

void COM_Color_RGB(int r, int g, int b)
	r,g,b:	absolute R/G/B values

void COM_Standard_color(int color)
	color:	standard color number (FIXED) or float color number (FLOAT)

int LIB_get_color_index(int color)
	color:	fixed color number (FIXED) or float color number (FLOAT)
	return:	internal color number

void LIB_get_color_index_array(int *dst, const int *src, int num)
	src:	fixed color numbers (FIXED) or float color numbers (FLOAT)
	dst:	internal color numbers

void LIB_assign_fixed_color(int user, int real)
	user:	fixed color number
	real:	internal color number

void LIB_assign_standard_color(int user, int real)
	user:	standard color number
	real:	internal color number

void COM_Reset_color(unsigned char r, unsigned char g, unsigned char b, int color)
	r,g,b:	absolute R/G/B values
	color:	fixed color number (FIXED) or float color number (FLOAT)

void COM_Reset_colors(
	int min, int max,
	const unsigned char *r,
	const unsigned char *g,
	const unsigned char *b)

	r,g,b:	absolute R/G/B values (array[0] defines min, array[max-min] defines max)
	min,max: fixed color numbers (FIXED) or float color numbers (FLOAT)

void COM_RGB_set_colors(const unsigned char *r, const unsigned char *g, const unsigned char *b)
	r,g,b:	index = logical R/G/B value, value = absolute R/G/B value

void COM_RGB_raster(
	int n, int nrows,
	const unsigned char *r, const unsigned char *g, const unsigned char *b,
	const unsigned char *nul)

	r,g,b:	logical R/G/B values
	nul:	nulls (zero -> non-null, non-zero -> null)

void COM_Raster_int(int num, int nrows, const int *array, int withzeros, int color_type)
void COM_Raster_int(int num, int nrows, const unsigned char *array, int withzeros, int color_type)
	array:	fixed color numbers (color_type != 0) or internal color numbers (color_type == 0)
	color_type: select fixed (non-zero) or internal (zero) color numbers