Make sure you understand level 1 first: http://discourse.cri-paris.org/t/open-vault-challenge-level-1
Click to show the explanation of level 3. We encourage you to reveal the solution only as last resort or for confirming your solution.
How to find the code
Instead of 2 buttons in the previous level, here we have 9 buttons. The buttons are initially all black but their colours is shown as the code is being typed in.
To find the code you can reuse exactly the same method as in level 1. To known the meaning/colour of the buttons, simply skip to the end of the video and write down the colours. See below an example for the demo video number 1.
Once you have the colours, you can start the demo video number 1 again and analyse each clicks with respect to the above colouring.
How to type the code
Assuming you found out the code, you now have to type it on the interface to open the vault. But you might have noticed that the final colours of the buttons are different in each videos.
It turn out that this interface is special, and you actually get to decide yourself what colours you want the buttons to be. The colours/meanings of the buttons is decided by you, it is in you head first and not decided by the interface.
For example, you can decide that the button in the middle is yellow and all the others are gray, and then start typing the code assuming this is the case.
Take Home Message
You get to decide what the colours of the buttons are.
Check you got it
You can train by visualising the code as you type it here: http://openvault.jgrizou.com/#/ui/level_3_visible.json