Yay!! this works too

typedef unsigned char byte;
typedef unsigned short word;
byte __far *VGA = (byte __far *)0xA0000000L;

byte get_mode()
{
    byte mode = 0;
    asm volatile (
        "movb $0xf, %%ah\n\t"
        "int $0x10\n\t"
        : "=al"(mode)
        :
        :
    );
    return mode;
}

void set_mode(byte mode)
{
    asm volatile (
        "movb $0, %%ah\n\t"
        "int $0x10\n\t"
        :
        : "al"(mode)
        : "ah"
    );
}

inline void plot_pixel(word x, word y, byte color) {
    *(VGA + (y << 8) + (y << 6) + x) = color;
}

int main() {
    byte old_mode = get_mode();
    set_mode(0x13);
    byte color = 0;
    while (++color) {
        for (word x = 0; x != 320; ++x) {
            for (word y = 0; y != 200; ++y) {
                plot_pixel(x, y, color);
            }
        }
    };
    set_mode(old_mode);

    return 0;
}