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Documentation Index

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Every color in LWXGL is referenced by a palette index from 0 to 15. When GCreateWindow runs, all 16 colors are allocated upfront as X11 colormap entries using XAllocColor. From that point on, every drawing call — text, buttons, primitives, image pixels — uses one of these 16 indices rather than raw RGB values. This indexed approach keeps the API simple and enables instant global theme changes: modifying a single palette slot immediately affects every element that references that index.

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Default Palette

The table below lists the 16 default colors as they are defined in the LWXGL source. These values are loaded at startup and can be changed at runtime with GPaletteModify.
IndexNameRGB
0Black000
1Dark Blue33173
2Dark Green01700
3Dark Cyan0168168
4Dark Red18666
5Dark Magenta1680168
6Orange23012634
7Light Gray168168168
8Dark Gray858783
9Light Blue8787255
10Light Green8525585
11Light Cyan96240240
12Light Red2558585
13Light Magenta24084240
14Yellow24424254
15White255255255
When designing UI colors, treat the 16-color palette like a CGA-style fixed set and build elements around index 0 (black) and index 15 (white) for maximum contrast. Indices 7 (light gray) and 8 (dark gray) are useful for secondary surfaces and disabled-state fills.

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Querying a Palette Entry

void GPaletteQuery(int idx, unsigned char *r, unsigned char *g, unsigned char *b);
Reads back the current RGB values for palette slot idx by querying the X server’s colormap directly. The results reflect any previous GPaletteModify calls, not the compile-time defaults. 
unsigned char r, g, b;
GPaletteQuery(1, &r, &g, &b);
printf("Palette slot 1: rgb(%d, %d, %d)\n", r, g, b);

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Modifying a Palette Entry

void GPaletteModify(int idx, unsigned char r, unsigned char g, unsigned char b, int redraw);
Replaces the X11 color allocation for slot idx with the new RGB values. The old pixel value is freed from the colormap and a new one is allocated in its place.
ParameterDescription
idxPalette index to replace (0–15)
r, g, bNew color components (0–255 each)
redrawPass 1 to call GRedrawAllImages() immediately, 0 to defer
Set redraw to 1 when you want image canvases to reflect the new color right away. Set it to 0 when you are changing multiple palette slots in a single frame — call GRedrawAllImages() manually after the last change to avoid redundant work. 
/* Replace dark blue (index 1) with a teal, and immediately redraw all images */
GPaletteModify(1, 0, 120, 200, 1);
Modifying a palette entry affects how all image pixels that use that index render. This includes every GCreateImage canvas currently in the element table. It does not affect the stored byte values in the pixel buffers — only the X11 color that those index values map to.

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Resetting the Palette

void GPaletteReset(void);
Frees all 16 current color allocations and reallocates them using the original compile-time default values shown in the table above. Always calls GRedrawAllImages() after restoring the palette. 
/* Undo any runtime palette changes */
GPaletteReset();

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How Colors Are Used in the API

Colors appear in three distinct forms across LWXGL’s API:

Single palette index

A plain integer 0–15 representing one color directly. Used by GCreateText (text color), image primitive functions (GPrimitiveLine, GPrimitiveCircle fill/border, etc.), GClearImage, GPrimitiveSprite, and the bgcol parameter of GCreateWindow.

Nibble-packed byte

A single int where the low nibble (bits 0–3) is the fill/background palette index and the high nibble (bits 4–7) is the border/outline palette index. Used by GCreateButton (unpressed/hover/pressed), GCreateInput (inactive/hover), GCreateCheckbox (cb_col), and GCreateRect — but note that GCreateRect accepts two separate plain indices for fg and bg rather than a packed byte.

Background color

The bgcol parameter passed to GCreateWindow is a single palette index used to clear the window background at the start of every GRenderWindow call.

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Runtime Palette Swap Example

The following example changes several palette slots to create a “night mode” theme, batching the redraws into a single call: 
void apply_night_mode(void) {
    /* Replace black (0) with a very dark navy */
    GPaletteModify(0, 10, 10, 30, 0);

    /* Replace white (15) with a warm off-white */
    GPaletteModify(15, 230, 220, 200, 0);

    /* Replace light gray (7) with a muted slate */
    GPaletteModify(7, 100, 110, 120, 0);

    /* Flush all image canvases once, after all changes */
    GRedrawAllImages();
}
To revert to the default colors at any time: 
GPaletteReset();

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