Hint:
Look at the minor potions standing on the table in Markunthar's room.
In case you greedy son of a bitch already picked them up:
<span class='standouttext'>Spoiler : </span><span class='spoiler'>
Press the buttons in this order: red-green-blue-yellow.
How do you find this combination? Look at the potions on the table: there's one red, two green, 3 blue and 4 yellow. </span>
