//CREATE:
col[room_width/64,room_height/64]=0
for (i=0; i<room_width/64; i+=1)
{
    for (j=0; j<room_height/64; j+=1)
    {
        col[i,j]=make_color_rgb(random(255),random(255),random(255))
    }
}

//DRAW:
for (i=0; i<room_width/64; i+=1)
{
    for (j=0; j<room_height/64; j+=1)
    {
        draw_set_color(col[i,j])
        draw_rectangle(i*64,j*64,(i*64)+64,(j*64)+64,true)
    }
}