for (i=0; i<room_width/64; i+=1)
{
    for (j=0; j<room_height; j+=1)
    {
        //Completely random color
        draw_set_color(make_color_rgb(random(255),random(255),random(255)))
        draw_rectangle(i*64,j*64,(i*64)+64,(j*64)+64,true)
    }
}