Hi cigar,
I don't have a save close to this point, unfortunately. What problem are you having with the box? Did you make sure to click on the cube painting out on the balcony? This is important.

This is how the painting looks:

This is how the box should look after you've clicked on the individual squares to change their colours:

Then click on the front green panel at bottom (where the padlock appears on the painting) to open the box.
