[Calisthenics]

pawn Code:

Color_GetBrightness(color)
{
    new r = ((color >> 24) & 0xFF) * 1000 / 255,
        g = ((color >> 16) & 0xFF) * 1000 / 255,
        b = ((color >> 8) & 0xFF) * 1000 / 255,
        
        max_value = max(max(r, g), b),
        min_value = min(min(r, g), b);
    
    return (max_value + min_value) / 20;
}

or

pawn Code:

RGB_GetBrightness(red_value, green_value, blue_value)
{
    new r = red_value * 1000 / 255,
        g = green_value * 1000 / 255,
        b = blue_value * 1000 / 255,

        max_value = max(max(r, g), b),
        min_value = min(min(r, g), b);
    
    return (max_value + min_value) / 20;
}

returns percentage (0-100) of brightness (ignoring alpha value, only used for client messages).

Example use:

pawn Code:

CMD:color(playerid, params[])
{
    new R, G, B;

    if (sscanf(params, "ddd", R, G, B)) return SendClientMessage(playerid, -1, "USAGE: /color <Red: 0-255> <Green: 0-255> <Blue: 0-255>");
    if (RGB_GetBrightness(R, G, B) <= 10) return SendClientMessage(playerid, -1, "ERROR: Choose a lighter color.");
 
    // create color and set for player
    return 1;
}